JP2018041669A - Electrode material, composite electrode material, negative electrode, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an electrode material which can suppress the decomposition of a nonaqueous electrolyte in a secondary battery; a composite electrode material; a negative electrode for a nonaqueous electrolyte secondary battery which includes any of them; and a nonaqueous electrolyte secondary battery.SOLUTION: An embodiment of the present invention is an electrode material for a nonaqueous electrolyte secondary battery, which comprises a carbon material of 40 Å or less in average pore diameter. Another embodiment of the invention is a composite electrode material for a nonaqueous electrolyte secondary battery, which comprises the electrode material. Another embodiment of the invention is a negative electrode for a nonaqueous electrolyte secondary battery, which comprises the electrode material or the composite electrode material. Another embodiment of the invention is a nonaqueous electrolyte secondary battery, which comprises the negative electrode.SELECTED DRAWING: None

Description

  The present invention relates to an electrode material, a composite electrode material, a negative electrode, and a nonaqueous electrolyte secondary battery.

  Nonaqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles and the like because of their high energy density. The nonaqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a nonaqueous electrolyte interposed between the electrodes, and transfers ions between the electrodes. It is comprised so that it may charge / discharge. The non-aqueous electrolyte usually contains a non-aqueous solvent, an electrolyte salt dissolved in the non-aqueous solvent, and other optional components added as necessary.

  As the electrode material of the nonaqueous electrolyte secondary battery, various carbon materials such as graphite and non-graphitizable carbon as a negative electrode active material, acetylene black and ketjen black as a conductive auxiliary agent are used. In addition, composite materials of carbon and metal have been developed as electrode materials. For example, in Patent Document 1, a porous carbon material and a metal material disposed on the surface of the porous carbon material are provided for the purpose of providing a negative electrode for a non-aqueous electrolyte battery excellent in charge / discharge cycle characteristics. A negative electrode for a non-aqueous electrolyte battery using a metal-carbon composite material is proposed. In the example of Patent Document 1, a porous carbon material having an average pore diameter of 4.1 nm (41 cm) is manufactured in order to obtain a metal carbon composite material.

JP 2010-277899 A

  In such conventional nonaqueous electrolyte secondary batteries, it is difficult to achieve both high initial coulomb efficiency and high initial discharge capacity. This may be caused by decomposition of a non-aqueous electrolyte (usually a non-aqueous solvent) during use or storage of the secondary battery. However, when the electrode which has the conventional carbon material is used, decomposition | disassembly of a nonaqueous electrolyte cannot fully be suppressed.

  The present invention has been made based on the circumstances as described above, and an object of the present invention is to provide an electrode material and a composite electrode material that can suppress the decomposition of the nonaqueous electrolyte in the secondary battery, and a nonaqueous solution containing these. To provide a negative electrode for an electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

  One embodiment of the present invention made to solve the above problems is an electrode material for a non-aqueous electrolyte secondary battery made of a carbon material having an average pore diameter of 40 mm or less.

  Another embodiment of the present invention is a composite electrode material for a non-aqueous electrolyte secondary battery including the electrode material.

  Another embodiment of the present invention is a negative electrode for a nonaqueous electrolyte secondary battery including a negative electrode active material layer containing the electrode material or the composite electrode material.

  Another embodiment of the present invention is a nonaqueous electrolyte secondary battery including the negative electrode.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode material and composite electrode material which can suppress decomposition | disassembly of the nonaqueous electrolyte in a secondary battery, the negative electrode for nonaqueous electrolyte secondary batteries containing these, and a nonaqueous electrolyte secondary battery are provided. can do.

FIG. 1 is an external perspective view showing a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a power storage device configured by assembling a plurality of nonaqueous electrolyte secondary batteries according to an embodiment of the present invention.

  The electrode material which concerns on 1 aspect of this invention is an electrode material for non-aqueous electrolyte secondary batteries which consists of a carbon material whose average pore diameter is 40 mm or less.

  By using the electrode material for the electrode of the non-aqueous electrolyte secondary battery, decomposition of the non-aqueous electrolyte in the secondary battery can be suppressed. The reason for this is not clear, but the following is presumed. When a conventional porous carbon material having a relatively large pore diameter is used for the electrode, the non-aqueous electrolyte penetrates into the pores, so that the contact area between the carbon material surface and the non-aqueous electrolyte is large. For this reason, the decomposition reaction of the nonaqueous electrolyte on the surface of the carbon material is likely to proceed. On the other hand, in the electrode material, the average pore diameter of the carbon material is 40 mm or less, and it is difficult for the nonaqueous electrolyte to penetrate into such fine pores. For this reason, when the electrode material is used for an electrode of a nonaqueous electrolyte secondary battery, the contact area between the carbon material surface and the nonaqueous electrolyte is reduced, and the decomposition reaction of the nonaqueous electrolyte on the carbon material surface is suppressed. Presumed to be.

“Average pore diameter” and “BET specific surface area” described later are values measured by the following methods. First, pore diameter distribution measurement using a nitrogen adsorption method is performed. This measurement can be performed by “autosorb iQ” manufactured by Quantachrome. Five points are extracted from the region of P / P0 = 0.06 to 0.3 of the obtained adsorption isotherm, a BET plot is performed, and the BET specific surface area is calculated from the y-intercept and slope of the straight line. Further, the pore volume is calculated from the total adsorbed gas amount in the pore size distribution measurement using the BJH method. Assuming that the pores are cylindrical, the pore volume V and the pore surface area A are expressed as follows.
V = π × (d / 2) ² × H
A = π × d × H
d: pore diameter, H: depth of the pore (equivalent to the height of the cylinder)
In the calculation of the surface area, the area of the surface corresponding to the bottom surface of the cylinder can be ignored. From the above two equations, d = 4 V / A is derived. Therefore, the average pore diameter d can be calculated from the equation d = 4 V / A using the values of the BET specific surface area A and the pore volume V.

It is preferable that the electrode material has a BET specific surface area of 100 m ² / g or more and 3,000 m ² / g or less. Thereby, the decomposition reaction of the nonaqueous electrolyte can be further suppressed while ensuring a sufficient surface area for charging and discharging.

  A composite electrode material according to another embodiment of the present invention is a composite electrode material for a non-aqueous electrolyte secondary battery including the electrode material.

  Since the composite electrode material contains a carbon material having an average pore diameter of 40 mm or less, the composite electrode material can be used for an electrode of a non-aqueous electrolyte secondary battery as in the case of the electrode material described above, so that the non-aqueous electrolyte in the secondary battery Decomposition can be suppressed.

  A negative electrode according to another embodiment of the present invention is a negative electrode for a nonaqueous electrolyte secondary battery including a negative electrode active material layer containing the electrode material or the composite electrode material.

  Since the negative electrode includes a negative electrode active material layer containing the electrode material or the composite electrode material, the use of the negative electrode in a non-aqueous electrolyte secondary battery can suppress decomposition of the non-aqueous electrolyte in the secondary battery. .

  The proportion of the carbon material contained in the negative electrode active material layer is preferably 30% by mass or more and 40% by mass or less. By making the content ratio of the carbon material within the above range, the irreversible capacity in charge / discharge can be reduced by sufficiently suppressing the reductive decomposition of the non-aqueous electrolyte and suppressing the isolation of other negative electrode active materials. You can also.

  A non-aqueous electrolyte secondary battery according to another embodiment of the present invention is a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “secondary battery”) including the negative electrode. In the secondary battery, since the electrode material or the composite material is used for the negative electrode, decomposition of the nonaqueous electrolyte can be suppressed. Therefore, according to the secondary battery, it is possible to achieve both high initial coulomb efficiency and high initial discharge capacity.

  Hereinafter, an electrode material, a composite electrode material, a negative electrode, and a secondary battery according to an embodiment of the present invention will be described in detail.

<Electrode material>
An electrode material according to an embodiment of the present invention is an electrode material for a non-aqueous electrolyte secondary battery made of a carbon material having an average pore diameter of 40 mm or less.

  The upper limit of the average pore diameter of the carbon material is preferably 37 mm, and more preferably 30 mm. By making the said average pore diameter below the said upper limit, the penetration | invasion into the pore of the carbon material of a nonaqueous electrolyte is suppressed more, and decomposition | disassembly of a nonaqueous electrolyte can be suppressed more.

  On the other hand, the lower limit of the average pore diameter of the carbon material is not particularly limited, and may be, for example, 1 Å, but is preferably 10 、, more preferably 20 、, even more preferably more than 25 、, and even more preferably 28 Å. By setting the pore diameter to the above lower limit or more, for example, when the electrode material functions as an active material, a surface area suitable for occlusion / release of ions such as lithium ions is secured, and charge / discharge characteristics can be improved.

The upper limit of the BET specific surface area of the carbon material is preferably 3,000 m ² / g, more preferably 1,500 m ² / g, more preferably ^{1,000m 2 / g, 500m 2 /} g and more preferably more, 250 m ² / g is even more preferable. By making the BET specific surface area of the said carbon material below the said upper limit, decomposition | disassembly of the nonaqueous electrolyte on a carbon material surface can be suppressed more.

On the other hand, the lower limit of the BET specific surface area of the carbon material, 100 m ² / g is preferable, 200 meters ² / g is more preferable. By setting the BET specific surface area of the carbon material to be equal to or higher than the lower limit, for example, when the electrode material functions as an active material, a surface area suitable for occlusion / release of ions such as lithium ions is secured, and charge / discharge characteristics are improved Etc. Further, by setting the BET specific surface area to be equal to or more than the above lower limit, for example, when the electrode material functions as a conductive agent, the contact area between the conductive agent and the active material is increased, thereby ensuring the electronic conductivity of the active material. In addition, the utilization rate and capacity maintenance rate of the active material can be increased.

  Although it does not specifically limit as a shape of the said electrode material, Usually, it is a powder form. Moreover, the said electrode material is comprised only from the said carbon material substantially. However, about the mixture of the said carbon material and another component, the effect similar to the said electrode material can be exhibited as a composite electrode material mentioned later.

  The electrode material can also function as a negative electrode active material that occludes and releases lithium ions and the like. In addition, the electrode material can be used together with another negative electrode active material or a positive electrode active material to function as a conductive additive. Furthermore, the said electrode material can also be used as a conductive support agent in the intermediate | middle layer of an electrode.

  Although it does not specifically limit as a manufacturing method of the said electrode material, For example, it can obtain by baking the organic type material containing a precursor polymer. More specifically, it can be obtained, for example, by mixing the precursor polymer, solvent and other additives to obtain the organic material, and drying and baking the organic material.

  Examples of the precursor polymer include polymers of aromatic vinyl monomers such as styrene and vinylphenol, and polymers of acrylic acid, methacrylic acid, or esters thereof. As said precursor polymer, the polymer of the monomer which has a hydroxyl group or a carboxy group is preferable, and polyvinyl phenol and polyacrylic acid are especially preferable. In such a polymer, it is considered that a carbon material having fine pores can be effectively obtained due to aggregation due to interaction between polar groups during drying and firing.

  The solvent is not particularly limited as long as it can dissolve the precursor polymer. Examples of the solvent include organic solvents such as N-methyl-2-pyrrolidone (NMP), xylene, toluene, cyclohexane, and ethanol, and NMP is preferable.

  Examples of the other additives include surfactants. By adding the surfactant, the dispersibility of the precursor polymer in the organic material is increased, and the electrode material having a small pore diameter can be obtained more effectively.

  Examples of the surfactant include anionic surfactants, cationic surfactants, and nonionic surfactants. Among these, nonionic surfactants are preferred, and polyoxyethylene polyoxy Nonionic surfactants having a polyol structure such as a propylene copolymer are more preferred. Such a surfactant can further enhance the dispersibility of the precursor polymer, and more effectively exhibits the aggregation action of the precursor polymer during the drying and firing described above. The material can be obtained efficiently.

  The lower limit of the substance amount (blending amount) of the surfactant is preferably 0.1 mol% of the substance amount of the precursor polymer structural unit (mass of precursor polymer / molecular weight of the structural unit), and 0.5 mol is preferable. More preferred. On the other hand, as this upper limit, 5 mol% is preferable and 2 mol% is more preferable. By using the surfactant in such a blending amount, a carbon material having fine pores can be obtained more effectively.

  As a minimum of content of an organic compound in solid content of the above-mentioned organic system material, 90 mass% is preferred, 99 mass% is more preferred, and 99.9 mass% is still more preferred. The content of the organic compound in the solid content of the organic material or the upper limit thereof may be 100% by mass. Thus, the pore diameter of the carbon material (electrode material) obtained can be reduced by using an organic material having a high organic compound content. The “solid content” refers to components other than the solvent. The “organic compound” refers to a compound containing a carbon atom.

  The drying can be performed at a temperature and time at which the solvent is sufficiently volatilized. In addition, drying and baking may be performed integrally or continuously.

  The firing is preferably performed in an inert gas atmosphere such as nitrogen gas. Moreover, as a minimum of baking temperature, 600 degreeC is preferable, 700 degreeC is more preferable, and 800 degreeC is further more preferable. On the other hand, the upper limit of the firing temperature is, for example, 1,200 ° C., preferably 1,000 ° C. The firing time can be, for example, 1 hour or more and 10 hours or less. In addition, you may perform preheating for about 1 hour or more and 5 hours or less, for example in the temperature range of 200 degreeC or more and 500 degrees C or less, before baking.

<Composite electrode material>
The composite electrode material which concerns on one Embodiment of this invention is a composite electrode material for nonaqueous electrolyte secondary batteries containing the said electrode material.

  In the composite electrode material, examples of the component other than the electrode material (carbon material having an average pore diameter of 40 mm or less) include metal materials and other carbon materials, but metal materials are preferable.

  Examples of the metal material include silicon, germanium, tin, indium, antimony, and zinc. The composite electrode material may be a particulate material in which the metallic material is coated with the particulate electrode material (carbon material having an average pore diameter of 40 mm or less), and the particulate electrode material, It may be a mixture with the particulate metal material. Such a composite electrode material containing the electrode material and the metal material can be suitably used as a negative electrode active material in a non-aqueous electrolyte secondary battery.

  Further, a positive electrode mixture or a negative electrode mixture containing the electrode material (a carbon material having an average pore diameter of 40 mm or less) is also an embodiment of the composite electrode material of the present invention.

  The content of the electrode material (carbon material having an average pore diameter of 40 mm or less) in the composite electrode material is not particularly limited, and the lower limit may be 1% by mass, 10% by mass, or 20%. The mass may be 40% by mass. Moreover, as this upper limit, it may be 99 mass%, may be 90 mass%, may be 80 mass%, and may be 50 mass%. In particular, when silicon is used as the negative electrode active material, the content of the electrode material with respect to the sum of silicon and the electrode material is preferably 30% by mass or more and 40% by mass or less. Within this range, the utilization rate of silicon can be increased, and reductive decomposition of the nonaqueous electrolyte can be suppressed while suppressing the isolation of silicon.

<Negative electrode>
The negative electrode which concerns on one Embodiment of this invention is a negative electrode for nonaqueous electrolyte secondary batteries containing the said electrode material or the said composite electrode material. The negative electrode includes a negative electrode base material and a negative electrode active material layer disposed on the negative electrode base material directly or via an intermediate layer. The negative electrode is usually a sheet having the above layer structure. The electrode material or the composite electrode material may be used as a negative electrode active material in the negative electrode active material layer or may be used as a conductive additive.

  The negative electrode substrate has conductivity. As a material of the negative electrode base material, a metal such as copper, nickel, stainless steel, nickel-plated steel, aluminum, or an alloy thereof is used, and copper or a copper alloy is preferable. Moreover, foil, a vapor deposition film, etc. are mentioned as a formation form of a negative electrode base material, and foil is preferable from the surface of cost. That is, copper foil is preferable as the negative electrode substrate. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The said intermediate | middle layer is a coating layer of the surface of a negative electrode base material, and reduces the contact resistance of a negative electrode base material and a negative electrode active material layer by including electroconductive particles, such as carbon particle. Note that the electrode material or the composite electrode material can also be used for the conductive particles. The structure of an intermediate | middle layer is not specifically limited, For example, it can form with the composition containing a resin binder and electroconductive particle. “Conductive” means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 ⁷ Ω · cm or less, and “nonconductive” Means that the volume resistivity is more than 10 ⁷ Ω · cm.

  The negative electrode active material layer is formed from a so-called negative electrode mixture containing a negative electrode active material. Moreover, the negative electrode composite material which forms a negative electrode active material layer contains arbitrary components, such as a conductive support agent, a binder (binder), a thickener, and a filler as needed.

  As the negative electrode active material, the electrode material or the composite electrode material described above can be used. As content of the negative electrode active material (the said electrode material or the said composite electrode material) in the said negative electrode active material layer, it can be 50 mass% or more and 95 mass% or less, for example. The lower limit of this content may be 60% by mass, and the upper limit of this content may be 90% by mass or 85% by mass. In addition, when using the said electrode material or the said composite electrode material as a negative electrode active material, a well-known electroconductive material can be used as said conductive support agent.

  Moreover, the said electrode material or the said composite electrode material can be used as said conductive support agent. In this case, as the negative electrode active material, a metal or a semimetal such as Si or Sn; a metal oxide or a semimetal oxide such as Si oxide or Sn oxide; a polyphosphate compound; graphite; Known negative electrode active materials such as carbonizable carbon or non-graphitizable carbon) can be used. As content of the conductive support agent in the said negative electrode active material layer, it can be 10 mass% or more and 50 mass% or less, for example.

  The lower limit of the content of the carbon material (the electrode material) having an average pore diameter of 40 mm or less in the negative electrode active material layer can be, for example, 10% by mass, and preferably 30% by mass. On the other hand, the upper limit of the carbon material content can be 50% by mass, and preferably 40% by mass. Note that silicon (Si) is preferably used as the negative electrode active material contained in the negative electrode active material layer. The lower limit of the silicon content in the negative electrode active material layer can be 20% by mass, but 40% by mass is preferable. Moreover, as an upper limit of this silicon content, although it can be 70 mass%, 50 mass% is preferable. Furthermore, as a minimum of content of the said carbon material with respect to the total content of the carbon material whose said average pore diameter in the said negative electrode active material layer is 40 or less, and silicon, 20 mass% is preferable and 35 mass% is more preferable. On the other hand, as an upper limit of this carbon material content, it can be 70 mass%, and 50 mass% is preferable. By including the electrode material and silicon in such a content in the negative electrode active material layer, the utilization rate of silicon is increased, and reductive decomposition of the nonaqueous electrolyte is suppressed while suppressing isolation of silicon. be able to. As a result, the irreversible capacity in charge / discharge can be reduced.

  Examples of the binder (binder) include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, polyimide; ethylene-propylene-diene rubber (EPDM), Examples thereof include elastomers such as sulfonated EPDM, styrene butadiene rubber (SBR) and fluororubber; polysaccharide polymers. As content of the binder in the said negative electrode active material layer, it can be 10 mass% or more and 30 mass% or less, for example.

  Examples of the thickener include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. When the thickener has a functional group that reacts with lithium, it is preferable to deactivate this functional group in advance by methylation or the like.

  The filler is not particularly limited as long as it does not adversely affect battery performance. Examples of the main component of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, and glass.

<Nonaqueous electrolyte secondary battery>
A secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, and the negative electrode according to an embodiment of the present invention described above is used as the negative electrode.

  The positive electrode and the negative electrode in the secondary battery usually form power generation elements that are alternately superimposed by stacking or winding via a separator. This power generation element is housed in a case, and the case is filled with a nonaqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Moreover, as said case, the well-known aluminum case, resin case, etc. which are normally used as a case of a nonaqueous electrolyte secondary battery can be used.

  The positive electrode has a positive electrode base material and a positive electrode active material layer disposed on the positive electrode base material directly or via an intermediate layer. The positive electrode usually has a sheet shape with the above layer structure. The intermediate layer can have the same configuration as the above-described negative electrode intermediate layer.

  The positive electrode base material has conductivity. As the material of the substrate, metals such as aluminum, titanium, tantalum, stainless steel, or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the balance of potential resistance, high conductivity and cost. Moreover, foil, a vapor deposition film, etc. are mentioned as a formation form of a positive electrode base material, and foil is preferable from the surface of cost. That is, an aluminum foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085P and A3003P defined in JIS-H-4000 (2014).

  The positive electrode active material layer is formed from a so-called positive electrode mixture containing a positive electrode active material. Moreover, the positive electrode mixture for forming the positive electrode active material layer includes optional components such as a conductive additive, a binder (binder), a thickener, and a filler as necessary. As these optional components, those similar to the negative electrode active material layer described above can be used.

As said positive electrode active material, a conventionally well-known thing is used as a positive electrode active material of a nonaqueous electrolysis secondary battery. As a specific positive electrode active material, for example, a composite oxide (Li _x having a layered α-NaFeO ₂ type crystal structure) represented by Li _x MO _y (M represents at least one transition metal other than Mo) is used. _{CoO 2, Li x NiO 2,} Li x MnO 3, Li x Ni α Co (1-α) O 2, Li x Ni α Mn β Co (1-α-β) O 2 or the like, having a spinel type crystal structure Li _x Mn ₂ O ₄ , Li _x Ni _α Mn _(2-α) O _4, etc.), Li _w M ′ _x (XO _y ) _z (M ′ represents at least one transition metal other than Mo, and X represents For example, polyanion compounds (LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoP) represented by P, Si, B, V, etc. O ₄ F etc.).

  As described above, the negative electrode according to an embodiment of the present invention is used for the negative electrode. The details of the negative electrode are as described above.

  As the material of the separator, for example, a woven fabric, a nonwoven fabric, a porous resin film, or the like is used. Among these, a porous resin film is preferable. The main component of the porous resin film is preferably a polyolefin such as polyethylene or polypropylene from the viewpoint of strength. Moreover, you may use the porous resin film which compounded these resins and resin, such as an aramid and a polyimide. A composite film in which a porous inorganic layer is laminated on a porous resin film can also be used.

  As the non-aqueous electrolyte, a known non-aqueous electrolyte usually used for a non-aqueous electrolyte secondary battery can be used. The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

  As said non-aqueous solvent, the well-known non-aqueous solvent normally used as a non-aqueous solvent of the general non-aqueous electrolyte for secondary batteries can be used. Examples of the non-aqueous solvent include cyclic carbonate, chain carbonate, ester, ether, amide, sulfone, lactone, and nitrile. Among these, it is preferable to use at least cyclic carbonate or chain carbonate, and it is more preferable to use cyclic carbonate and chain carbonate in combination.

  When the cyclic carbonate and the chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is not particularly limited, but is, for example, 5:95 or more and 50:50 or less. Is more preferable, and 20:80 or more and 40:60 or less is more preferable. By using a non-aqueous solvent having such a mixing ratio, the viscosity and the like are optimized, so that the penetration into the electrode material made of a carbon material having an average pore diameter of 40 mm or less is further suppressed, and a non-aqueous solvent ( Decomposition of the nonaqueous electrolyte is further suppressed.

  Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene. Examples include carbonate (DFEC), styrene carbonate, catechol carbonate, 1-phenyl vinylene carbonate, 1,2-diphenyl vinylene carbonate, and among these, EC is preferable.

  Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diphenyl carbonate. Among these, DMC and EMC are preferable.

Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt, and the like, but lithium salt is preferable. Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO Fluorohydrocarbon groups such as ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) ₃ A lithium salt having

  Other additives may be added to the non-aqueous electrolyte. Moreover, room temperature molten salt, ionic liquid, polymer solid electrolyte, etc. can also be used as the non-aqueous electrolyte.

  Although the manufacturing method of the secondary battery is not particularly limited, for example, it includes a step of producing an electrode body including a positive electrode and a negative electrode, a step of housing the electrode body in a case, and a step of injecting a nonaqueous electrolyte into the case. . Each said process can be performed by a well-known method. After the injection, the non-aqueous electrolyte secondary battery can be obtained by sealing the injection port.

<Other embodiments>
The present invention is not limited to the above-described embodiment, and can be implemented in a mode in which various changes and improvements are made in addition to the above-described mode.

  In FIG. 1, the schematic of the rectangular nonaqueous electrolyte secondary battery 1 which is one Embodiment of the said nonaqueous electrolyte secondary battery is shown. In the figure, the inside of the container is seen through. In the nonaqueous electrolyte secondary battery 1 shown in FIG. 1, an electrode body 2 is housed in a battery container 3 (case). The electrode body 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′.

  The configuration of the non-aqueous electrolyte secondary battery is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), a flat battery, and the like. The present invention can also be realized as a power storage device including a plurality of the above non-aqueous electrolyte secondary batteries. One embodiment of a power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

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

[Example 1]
In NMP, a precursor polymer, polyvinylphenol (PVP), and a surfactant, polyoxyethylene polyoxypropylene copolymer ("Pluronic F-127" from Sigma-Aldrich, weight average molecular weight 12,600) are dissolved. To obtain an organic material. The surfactant was used at a blending ratio such that the amount of the substance was 1 mol% of the amount of the precursor polymer structural unit (the mass of the precursor polymer / the molecular weight of the structural unit). This organic material was dried at 120 ° C. to obtain a powder. The obtained powder was held at 400 ° C. for 3 hours under a nitrogen gas atmosphere, and then calcined at 700 ° C. for 3 hours to obtain an electrode material of Example 1 as a carbon material.

[Example 2]
An electrode material of Example 2 was obtained in the same manner as Example 1 except that the precursor polymer was polyacrylic acid (PAA) and the firing temperature was 900 ° C.

[Comparative Example 1]
NMP includes precursor polymer PVP, surfactant polyoxyethylene polyoxypropylene copolymer ("Pluronic F-127" of Sigma-Aldrich): weight average molecular weight 12,600, and MgO template. Magnesium acetate was dissolved or dispersed to obtain an organic material. The surfactant was used at a blending ratio such that the amount of the substance was 1 mol% of the amount of the precursor polymer structural unit (the mass of the precursor polymer / the molecular weight of the structural unit). Moreover, the compounding quantity of magnesium acetate was 20 mass parts with respect to 100 mass parts of precursor polymers. This organic material was dried at 120 ° C. to obtain a powder. The obtained powder was held at 400 ° C. for 3 hours under a nitrogen gas atmosphere and then calcined at 700 ° C. for 3 hours. The fired powder was dispersed in a 1M sulfuric acid aqueous solution overnight, then filtered, and dried overnight at 100 ° C. to remove MgO as a mold to obtain an electrode material of Comparative Example 1 as a carbon material. .

[Comparative Example 2]
An electrode material of Comparative Example 2 was obtained in the same manner as in Comparative Example 1 except that the amount of magnesium acetate was 35 parts by mass with respect to 100 parts by mass of the precursor polymer.

[Comparative Example 3]
Commercially available acetylene black was used as the electrode material of Comparative Example 3.

[Measurement]
About each electrode material (carbon material) of the said Example and comparative example, the average pore diameter and the BET specific surface area were measured by the method mentioned above. The measurement results are shown in Table 1.

[Evaluation]
An electrode mixture was prepared by mixing each of the above electrode materials and a polyacrylic acid binder at a mass ratio of 80:20. This electrode mixture was applied to a disk-shaped (diameter 12 mm) nickel mesh substrate to prepare a working electrode (negative electrode). On the other hand, metallic lithium having a disk shape (diameter 16 mm, thickness 300 μm) was used as a counter electrode (positive electrode). Further, LiPF ₆ was dissolved at a concentration of 1M in a non-aqueous solvent in which EC, EMC, and DMC were mixed at a volume ratio of 30:35:35 to prepare a non-aqueous electrolyte. An evaluation cell as a nonaqueous electrolyte secondary battery was produced using the obtained working electrode, counter electrode and nonaqueous electrolyte (80 μl).

The obtained evaluation cell was subjected to constant current and constant voltage (CCCV) charging at 0.1 C and a cutoff voltage of 0.02 V (vs. Li / Li ⁺ ). 1C was based on a theoretical capacity of 372 mAhg ^{−1 of} graphite. While maintaining the potential of the working electrode at 0.02 V (vs. Li / Li ⁺ ), the electrode was allowed to stand for 10 days, and the amount of electricity that flowed in 10 days was measured. Table 1 shows values obtained by converting the amount of electricity into the amount of electricity per unit mass of the electrode material.

  As shown in Table 1, in Examples 1 and 2, the amount of electricity that flowed in 10 days (value of the amount of electricity per unit mass of electrode material) is small. This amount of electricity is generated by decomposition of a nonaqueous electrolyte such as a nonaqueous solvent. In Examples 1 and 2, it can be seen that decomposition of the nonaqueous electrolyte is sufficiently suppressed. In Examples 1 and 2, the average pore diameter is as very small as 40 mm or less, so that it is presumed that the penetration of the nonaqueous electrolyte into the pores is suppressed and decomposition is hardly caused. The specific surface area of Examples 1 and 2 is larger than the specific surface areas of Comparative Examples 1 to 3 because the larger the specific surface area is, the easier the decomposition reaction on the carbon material surface occurs. Therefore, it is considered that the above-described effect that the decomposition of the nonaqueous electrolyte is suppressed is a unique effect that is exhibited by setting the average pore diameter to 40 mm or less.

[Example 3]
A negative electrode mixture in which the metal silicon powder, the electrode material obtained in Example 1 and the polyacrylic acid binder were contained at a mass ratio of 70:10:20 and NMP was used as a dispersion medium was produced. An evaluation cell of Example 3 was produced in the same manner as in the above [Evaluation] except that this negative electrode mixture was used.

[Example 4]
An evaluation cell of Example 4 was produced in the same manner as in Example 3 except that the mass ratio of the metal silicon powder, the electrode material obtained in Example 1 and the polyacrylic acid binder was 60:20:20.

[Example 5]
An evaluation cell of Example 5 was produced in the same manner as in Example 3 except that the mass ratio of the metal silicon powder, the electrode material obtained in Example 1 and the polyacrylic acid binder was 50:30:20.

[Example 6]
An evaluation cell of Example 6 was produced in the same manner as in Example 3 except that the mass ratio of the metal silicon powder, the electrode material obtained in Example 1 and the polyacrylic acid binder was 40:40:20.

[Comparative Example 4]
An evaluation cell of Comparative Example 4 was produced in the same manner as in Example 3 except that the mass ratio of the metal silicon powder, acetylene black, and polyacrylic acid binder was 67:13:20.

[Comparative Example 5]
An evaluation cell of Comparative Example 5 was produced in the same manner as in Example 3 except that the mass ratio of the metal silicon powder, acetylene black and polyacrylic acid binder was 53:27:20.

[Comparative Example 6]
An evaluation cell of Comparative Example 6 was produced in the same manner as in Example 3 except that the mass ratio of the metal silicon powder, acetylene black, and polyacrylic acid binder was 40:40:20.

About the obtained evaluation cell, the charging / discharging test was done in the thermostat set to 25 degreeC. Charging was constant current constant voltage (CCCV) charging, the charging lower limit potential was 0.02 V (vs. Li / Li ⁺ ), and the total charging time was 20 hours. The discharge was a constant current (CC) discharge, and the discharge end potential was 1.2 V (vs. Li ^/ Li ⁺ ). The constant current values for charging and discharging were set at 0.1 C, assuming that 4200 mAh / g, which is the theoretical capacity of metal silicon, was 1 C. In each cycle, a pause time of 10 minutes was set after charging and discharging. This cycle was carried out 10 times. For each evaluation cell, the initial utilization rate of silicon, the cumulative irreversible capacity derived from SEI (Solid Electrolyte Interphase) formation, and the cumulative irreversible capacity derived from silicon isolation were calculated as follows. These values are shown in Table 2.

  The initial utilization rate of silicon was calculated by dividing the discharge capacity at the first cycle by the mass of the metal silicon powder and then dividing by the theoretical capacity of metal silicon, 4200 mAh / g.

  The irreversible capacity resulting from the formation of SEI at the time of charging in the second cycle can be obtained by subtracting the discharge capacity in the first cycle from the amount of charged electricity in the second cycle. The value obtained by integrating the irreversible capacity derived from the SEI formation at the nth cycle (n ≧ 2) thus obtained was calculated as the cumulative irreversible capacity derived from the SEI formation. The irreversible capacity in the charge / discharge reaction of silicon is considered to be the sum of the irreversible capacity derived from the formation of SEI and the irreversible capacity derived from the isolation of silicon. The capacity is obtained by subtracting the irreversible capacity derived from the SEI formation at the nth cycle from the irreversible capacity at the nth cycle. Therefore, the cumulative irreversible capacity derived from the isolation of silicon was calculated by subtracting the cumulative irreversible capacity derived from SEI formation from the accumulated value of the irreversible capacity up to the 10th cycle.

  As shown in Table 2, in Examples 3 to 6, the total irreversible capacity is smaller than in Comparative Examples 4 to 6. This is due to the small cumulative irreversible capacity derived from SEI formation. From this, in Examples 3-6, it turns out that decomposition | disassembly of a nonaqueous electrolyte is suppressed. In Examples 5 and 6, compared to Examples 3 and 4, in addition to a small irreversible capacity, the initial utilization rate of silicon is high. Therefore, when the electrode material according to the present embodiment is used in a mixture with a negative electrode active material, particularly silicon, the electrode material is preferably 30% by mass or more and 40% by mass or less of the negative electrode active material layer.

  INDUSTRIAL APPLICABILITY The present invention can be used for electronic devices such as personal computers and communication terminals, nonaqueous electrolyte secondary batteries used as power sources for automobiles, the negative electrode provided therein, and materials thereof.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Electrode body 3 Battery container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 Power storage unit 30 Power storage device

Claims (6)

  An electrode material for a non-aqueous electrolyte secondary battery comprising a carbon material having an average pore diameter of 40 mm or less. ^2. The electrode material according to claim 1, wherein the BET specific surface area is 100 m ² / g or more and 3,000 m ² / g or less.   The composite electrode material for nonaqueous electrolyte secondary batteries containing the electrode material of Claim 1 or Claim 2.   A negative electrode for a nonaqueous electrolyte secondary battery comprising a negative electrode active material layer comprising the electrode material of claim 1 or claim 2 or the composite electrode material of claim 3.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 4, wherein the proportion of the carbon material contained in the negative electrode active material layer is 30% by mass or more and 40% by mass or less.   A nonaqueous electrolyte secondary battery comprising the negative electrode according to claim 4 or 5.

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