JP6733443B2 - Composite electrode material, negative electrode, and non-aqueous electrolyte secondary battery - Google Patents

Description

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

Non-aqueous electrolyte secondary batteries represented 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 non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between both electrodes. Therefore, it is configured to be charged and discharged. The non-aqueous electrolyte usually contains a non-aqueous solvent, an electrolyte salt dissolved in this non-aqueous solvent, and other optional components added as necessary.

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

JP, 2010-277989, A

In such conventional non-aqueous electrolyte secondary batteries, it is difficult to achieve both high initial Coulombic efficiency and high initial discharge capacity. The cause of this may be decomposition of the non-aqueous electrolyte (usually a non-aqueous solvent) during use or storage of the secondary battery. However, when an electrode having a conventional carbon material is used, decomposition of the non-aqueous electrolyte cannot be suppressed sufficiently.

The present invention has been made based on the above circumstances, and an object thereof is an electrode material and a composite electrode material capable of suppressing decomposition of a non-aqueous electrolyte in a secondary battery, and a non-aqueous material containing these. 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 Å or less.

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

Another embodiment of the present invention is a negative electrode for a non-aqueous 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 non-aqueous 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 non-aqueous electrolyte in a secondary battery, the negative electrode for non-aqueous electrolyte secondary batteries containing these, and a non-aqueous electrolyte secondary battery are provided. can do.

FIG. 1 is an external perspective view showing a non-aqueous 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 non-aqueous electrolyte secondary batteries according to an embodiment of the present invention.

The electrode material according to one embodiment of the present invention is an electrode material for a non-aqueous electrolyte secondary battery, which is made of a carbon material having an average pore diameter of 40 Å or less.

By using the electrode material for the electrode of the non-aqueous electrolyte secondary battery, the 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 size is used for the electrode, the non-aqueous electrolyte permeates into the pores, so that the contact area between the surface of the carbon material and the non-aqueous electrolyte is large. Therefore, the decomposition reaction of the non-aqueous electrolyte on the surface of the carbon material easily proceeds. On the other hand, in the electrode material, the average pore diameter of the carbon material is 40 Å or less, and it becomes difficult for the nonaqueous electrolyte to permeate into such fine pores. Therefore, when the electrode material is used for an electrode of a non-aqueous electrolyte secondary battery, the contact area between the carbon material surface and the non-aqueous electrolyte becomes small, and the decomposition reaction of the non-aqueous electrolyte on the carbon material surface is suppressed. Presumed to be present.

The "average pore diameter" and the "BET specific surface area" described later are values measured by the following method. First, the pore size distribution is measured using the nitrogen adsorption method. This measurement can be performed by "autosorb iQ" manufactured by Quantachrome. BET plot is performed by extracting 5 points from the region of P/P0=0.06 to 0.3 of the obtained adsorption isotherm, and the BET specific surface area is calculated from the y-intercept and slope of the straight line. Further, the pore volume is calculated using the BJH method from the total amount of adsorbed gas in the pore size distribution measurement. Assuming that the pores are cylindrical, the volume V of the pores and the surface area A of the pores are expressed as follows.
V=π×(d/2) ² ×H
A=π×d×H
d: Pore diameter, H: Pore depth (corresponding to the height of the cylinder)
In calculating 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=4V/A is derived. Therefore, the average pore diameter d can be calculated from the equation of d=4V/A using the values of the BET specific surface area A and the pore volume V.

The BET specific surface area of the electrode material is preferably 100 m ² /g or more and 3,000 m ² /g or less. This makes it possible to further suppress the decomposition reaction of the non-aqueous electrolyte while ensuring a surface area sufficient for charge/discharge.

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

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

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

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

The ratio 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 setting the content ratio of the carbon material in the above range, by sufficiently suppressing the reductive decomposition of the non-aqueous electrolyte, it is possible to suppress the isolation of the other negative electrode active material, etc., to reduce the irreversible capacity in charge and discharge. Can also

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

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

The upper limit of the average pore diameter of the carbon material is preferably 37Å, more preferably 30Å. By setting the average pore diameter to be equal to or less than the upper limit, it is possible to further suppress the nonaqueous electrolyte from entering the pores of the carbon material and further suppress the decomposition of the nonaqueous electrolyte.

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 10 Å is preferable, 20 Å is more preferable, more than 25 Å is further preferable, and 28 Å is further preferable. 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 storage and release of ions such as lithium ions can be secured, and charge/discharge characteristics can be improved.

As an upper limit of the BET specific surface area of the above carbon material, 3,000 m ² /g is preferable, 1,500 m ² /g is more preferable, 1,000 m ² /g is further preferable, 500 m ² /g is still more preferable, 250 m ² /g is even more preferred. By setting the BET specific surface area of the carbon material to be equal to or less than the upper limit, it is possible to further suppress the decomposition of the non-aqueous electrolyte on the surface of the carbon material.

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 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 are improved. And so on. Further, by setting the BET specific surface area to the above lower limit or more, for example, when the electrode material functions as a conductive agent, the contact area between the conductive agent and the active material increases, so that the electron conductivity of the active material is secured. It is possible to increase the utilization rate of active material and the capacity retention rate.

The shape of the electrode material is not particularly limited, but is usually powdery. Moreover, the said electrode material is comprised substantially only from the said carbon material. However, a mixture of the above carbon material and other components can exhibit the same effect as the electrode material as a composite electrode material described later.

The electrode material can also function as a negative electrode active material that absorbs and releases lithium ions and the like. In addition, the electrode material can be used together with other negative electrode active material or positive electrode active material to function as a conduction aid. Further, the electrode material can be used as a conductive auxiliary agent in the intermediate layer of the electrode.

The method for producing the electrode material is not particularly limited, but it can be obtained, for example, by firing an organic material containing a precursor polymer. More specifically, for example, it can be obtained by mixing the precursor polymer, the solvent and other additives to obtain the organic material, and drying and firing 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 their esters. As the precursor polymer, a polymer of a monomer having a hydroxyl group or a carboxy group is preferable, and among them, polyvinylphenol and polyacrylic acid are preferable. It is considered that such a polymer can effectively obtain a carbon material having fine pores 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 above-mentioned other additives include surfactants. By adding the surfactant, the dispersibility of the precursor polymer in the organic material is enhanced, and the electrode material having a small pore size can be obtained more effectively.

Examples of the above-mentioned surfactant include anionic surfactants, cationic surfactants, nonionic surfactants and the like. Among these, nonionic surfactants are preferable, and polyoxyethylene polyoxy A nonionic surfactant having a polyol structure such as a propylene copolymer is more preferable. Such a surfactant can further enhance the dispersibility of the precursor polymer, and more effectively exhibit the aggregation action of the precursor polymer during the above-mentioned drying and firing, thereby making the electrode 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 structural unit of the precursor polymer (mass of the precursor polymer/molecular weight of the structural unit), and 0.5 mol is preferable. More preferable. On the other hand, the upper limit is preferably 5 mol%, more preferably 2 mol%. By using the surfactant in an amount within such a range, it is possible to more effectively obtain a carbon material having fine pores.

As a minimum of content of the organic compound in solid content of the above-mentioned organic 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. As described above, by using the organic material having a high content of the organic compound, the pore diameter of the obtained carbon material (electrode material) can be reduced. In addition, "solid content" means a component other than a solvent. Moreover, an "organic compound" means a compound containing a carbon atom.

The above drying can be performed at a temperature and for a time at which the solvent is sufficiently volatilized. The drying and firing may be performed integrally or continuously.

The firing is preferably performed in an inert gas atmosphere such as nitrogen gas. The lower limit of the firing temperature is preferably 600°C, more preferably 700°C, even more preferably 800°C. On the other hand, the upper limit of the firing temperature is, for example, 1,200°C, preferably 1,000°C. The firing time may be, for example, 1 hour or more and 10 hours or less. Before firing, preheating may be performed, for example, in a temperature range of 200° C. or higher and 500° C. or lower for 1 hour or more and 5 hours or less.

<Composite electrode material>
A composite electrode material according to an embodiment of the present invention is a composite electrode material for a non-aqueous electrolyte secondary battery containing the electrode material.

In the composite electrode material, examples of components other than the electrode material (carbon material having an average pore diameter of 40 Å 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, zinc and the like. The composite electrode material may be a particulate electrode material (a carbon material having an average pore size of 40Å or less) coated with the metal material, or the particulate electrode material, It may be a mixture with the metallic material in the form of particles. 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 composite material or a negative electrode composite material containing the electrode material (a carbon material having an average pore diameter of 40 Å 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 size of 40Å 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% by mass. It may be mass% or may be 40 mass %. The upper limit may be 99% by mass, 90% by mass, 80% by mass, or 50% by mass. Particularly 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 the reductive decomposition of the non-aqueous electrolyte can be suppressed while suppressing the isolation of silicon.

<Negative electrode>
A negative electrode according to an embodiment of the present invention is a negative electrode for a non-aqueous electrolyte secondary battery containing the electrode material or the composite electrode material. The negative electrode has a negative electrode base material and a negative electrode active material layer arranged on the negative electrode base material directly or via an intermediate layer. The negative electrode is usually in the form of 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 base material has conductivity. As the material of the negative electrode base material, metals such as copper, nickel, stainless steel, nickel plated steel, and aluminum or alloys thereof are used, and copper or copper alloy is preferable. In addition, examples of the form of forming the negative electrode base material include a foil and a vapor deposition film, and the foil is preferable from the viewpoint of cost. That is, copper foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The intermediate layer is a coating layer on the surface of the negative electrode base material, and contains conductive particles such as carbon particles to reduce the contact resistance between the negative electrode base material and the negative electrode active material layer. The electrode material or the composite electrode material may be used for the conductive particles. The structure of the intermediate layer is not particularly limited, and can be formed of, for example, a composition containing a resin binder and conductive particles. In addition, having "conductivity" means that the volume resistivity measured according to JIS-H-0505 (1975) is 10 ⁷ Ω·cm or less, and is "non-conducting". Means that the above volume resistivity is more than 10 ⁷ Ω·cm.

The negative electrode active material layer is formed of a so-called negative electrode mixture containing the negative electrode active material. Further, the negative electrode mixture material forming the negative electrode active material layer contains optional components such as a conductive auxiliary agent, a binder (binder), a thickener, and a filler, if necessary.

As the negative electrode active material, the electrode material or the composite electrode material described above can be used. The content of the negative electrode active material (the electrode material or the composite electrode material) in the negative electrode active material layer can be, for example, 50% by mass or more and 95% by mass or less. The lower limit of this content may be 60% by weight and the upper limit of this content may be 90% by weight or 85% by weight. When the electrode material or the composite electrode material is used as the negative electrode active material, a known conductive material can be used as the conductive additive.

Moreover, the said electrode material or the said composite electrode material can be used as said conductive auxiliary agent. In this case, as the negative electrode active material, metals such as Si and Sn or semimetals; metal oxides or semimetal oxides such as Si oxides and Sn oxides; polyphosphoric acid compounds; graphite; amorphous carbon (easy graphite) A known negative electrode active material such as a volatile carbon or a non-graphitizable carbon) can be used. The content of the conductive additive in the negative electrode active material layer may be, for example, 10% by mass or more and 50% by mass or less.

The lower limit of the content of the carbon material (the electrode material) having an average pore diameter of 40 Å 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 40% by mass is preferable. Note that it is preferable to use silicon (Si) as the negative electrode active material contained in the negative electrode active material layer. The lower limit of the content of silicon in the negative electrode active material layer may be 20% by mass, but 40% by mass is preferable. The upper limit of the silicon content may be 70% by mass, but 50% by mass is preferable. Further, the lower limit of the content of the carbon material with respect to the total content of the carbon material having the average pore diameter of 40 Å or less and silicon in the negative electrode active material layer is preferably 20% by mass, and more preferably 35% by mass. On the other hand, the upper limit of the carbon material content can be 70% by mass, and 50% by mass is preferable. In the negative electrode active material layer, by containing the electrode material and silicon in such a content, while increasing the utilization rate of silicon, while suppressing the isolation of silicon, suppress the reductive decomposition of the non-aqueous electrolyte be able to. Further, as a result, the irreversible capacity during 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), Elastomers such as sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; polysaccharide polymers and the like. The content of the binder in the negative electrode active material layer can be, for example, 10% by mass or more and 30% by mass or less.

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

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

<Non-aqueous 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 the above-described embodiment of the present invention is used as the negative electrode.

The positive electrode and the negative electrode in the secondary battery usually form a power generation element that is alternately stacked by stacking or winding via a separator. The power generating element is housed in a case, and the nonaqueous electrolyte is filled in the case. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the case, a known aluminum case, resin case, or the like that is usually used as a case of a non-aqueous electrolyte secondary battery can be used.

The positive electrode has a positive electrode base material and a positive electrode active material layer arranged on the positive electrode base material directly or via an intermediate layer. The positive electrode usually has a sheet shape having the above layer structure. The intermediate layer may have the same structure as the intermediate layer of the negative electrode described above.

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

The positive electrode active material layer is formed of a so-called positive electrode mixture containing a positive electrode active material. In addition, the positive electrode mixture material forming the positive electrode active material layer contains optional components such as a conductive auxiliary agent, a binder (binder), a thickener, and a filler, if necessary. As these optional components, those similar to the above-mentioned negative electrode active material layer can be used.

As the positive electrode active material, a conventionally known positive electrode active material for a non-aqueous electrolytic secondary battery is used. As a specific positive electrode active material, for example, a composite oxide represented by Li _x MO _y (M represents at least one transition metal other than Mo) (Li _x having a layered α-NaFeO ₂ type crystal structure) _{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, X is For example, polyanion compounds represented by P, Si, B, V, etc. (LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄₎ F and the like).

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

As the material of the separator, for example, woven cloth, non-woven cloth, porous resin film or the like is used. Of these, a porous resin film is preferable. The main component of the porous resin film is preferably 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 aramid and polyimide. Further, 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 that is usually used in non-aqueous electrolyte secondary batteries can be used. The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

As the non-aqueous solvent, a known non-aqueous solvent that is usually used as a non-aqueous solvent for a 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 and 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 preferred, and more preferably 20:80 or more and 40:60 or less. By using the non-aqueous solvent having such a mixing ratio, the viscosity and the like are optimized, so that the permeation into the electrode material made of a carbon material having an average pore diameter of 40 Å or less is further suppressed, and the non-aqueous solvent ( The decomposition of the non-aqueous 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), difluoroethylene. Carbonate (DFEC), styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate and the like can be mentioned, and among these, EC is preferable.

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

Examples of the electrolyte salt include a lithium salt, a sodium salt, a potassium salt, a magnesium salt, an onium salt and the like, and a 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 and LiN(SO. _{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 fluorinated hydrocarbon group, Examples thereof include a lithium salt having

Other additives may be added to the non-aqueous electrolyte. Further, as the non-aqueous electrolyte, a room temperature molten salt, an ionic liquid, a polymer solid electrolyte, or the like can be used.

The method for manufacturing the secondary battery is not particularly limited, but includes, for example, a step of manufacturing 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 non-aqueous electrolyte into the case. .. Each of the above steps can be performed by a known method. After injection, the injection port is sealed to obtain a non-aqueous electrolyte secondary battery.

<Other embodiments>
The present invention is not limited to the above embodiment, and can be carried out in various modified and improved modes other than the above modes.

FIG. 1 shows a schematic view of a rectangular non-aqueous electrolyte secondary battery 1 which is an embodiment of the non-aqueous electrolyte secondary battery. It should be noted that the figure is a perspective view of the inside of the container. In the non-aqueous electrolyte secondary battery 1 shown in FIG. 1, the 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 with a separator interposed therebetween. 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 prismatic battery (rectangular battery), and a flat battery. The present invention can also be realized as a power storage device including a plurality of the above non-aqueous electrolyte secondary batteries. An embodiment of the 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 non-aqueous electrolyte secondary batteries 1. The power storage device 30 can be installed as a power source for vehicles such as electric vehicles (EV), hybrid vehicles (HEV), and plug-in hybrid vehicles (PHEV).

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

[Example 1]
Polyvinylphenol (PVP) which is a precursor polymer and polyoxyethylene polyoxypropylene copolymer (“Pluronic F-127” manufactured by Sigma-Aldrich: weight average molecular weight 12,600) which is a surfactant are dissolved in NMP. Then, an organic material was obtained. The surfactant was used at a compounding ratio such that the amount of the substance was 1 mol% of the amount of the substance of the structural unit of the precursor polymer (mass of the precursor polymer/molecular weight of the structural unit). This organic material was dried at 120° C. to obtain a powder. The obtained powder was kept under a nitrogen gas atmosphere at 400° C. for 3 hours and then calcined at 700° C. for 3 hours to obtain an electrode material of Example 1 which was a carbon material.

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

[Comparative Example 1]
NMP, a precursor polymer PVP, a surfactant polyoxyethylene polyoxypropylene copolymer ("Pluronic F-127" manufactured by Sigma-Aldrich Co.: weight average molecular weight 12,600), and a MgO template. Magnesium acetate was dissolved or dispersed to obtain an organic material. The surfactant was used at a compounding ratio such that the amount of the substance was 1 mol% of the amount of the substance of the structural unit of the precursor polymer (mass of the precursor polymer/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 in a nitrogen gas atmosphere, and then fired at 700° C. for 3 hours. The calcined powder was dispersed in a 1M sulfuric acid aqueous solution overnight, filtered, and dried overnight at 100° C. to remove MgO as a template, thereby obtaining 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 Comparative Example 1 except that the content 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]
The average pore diameter and the BET specific surface area of each electrode material (carbon material) of the above-mentioned Examples and Comparative Examples were measured by the above-mentioned methods. The measurement results are shown in Table 1.

[Evaluation]
An electrode mixture was prepared by mixing the above electrode materials and a polyacrylic acid binder in a mass ratio of 80:20. This electrode mixture was applied on a nickel mesh base material having a disk shape (diameter 12 mm) to prepare a working electrode (negative electrode). On the other hand, disk-shaped (diameter 16 mm, thickness 300 μm) metallic lithium was used as the counter electrode (positive electrode). Further, LiPF ₆ was dissolved at a concentration of 1 M 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 non-aqueous electrolyte secondary battery was prepared using the obtained working electrode, counter electrode and non-aqueous electrolyte (80 μl).

The obtained evaluation cell was subjected to constant current constant voltage (CCCV) charging (Lithiation) at 0.1 C and a cutoff voltage of 0.02 V (vs. Li/Li ⁺ ). Note that 1 C is based on the theoretical capacity of graphite of 372 mAhg ⁻¹ . While keeping 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 flowing for 10 days was measured. Table 1 shows the value of this amount of electricity converted 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 (value of the amount of electricity per unit mass of the electrode material) flowing in 10 days was small. This amount of electricity is generated by the decomposition of the non-aqueous electrolyte such as the non-aqueous solvent, and in Examples 1 and 2, it can be seen that the decomposition of the non-aqueous electrolyte is sufficiently suppressed. In Examples 1 and 2, the average pore diameter is 40 Å or less, which is extremely small, and it is presumed that this prevents the nonaqueous electrolyte from penetrating into the pores and makes decomposition less likely to occur. It is considered that the larger the specific surface area, the more easily the decomposition reaction on the surface of the carbon material occurs, but the specific surface areas of Examples 1 and 2 are larger than the specific surface areas of Comparative Examples 1 to 3. Therefore, the above-mentioned effect of suppressing the decomposition of the non-aqueous electrolyte is considered to be a unique effect exhibited by setting the average pore diameter to 40 Å or less.

[Example 3]
A negative electrode mixture containing NMP as a dispersion medium was prepared by including metal silicon powder, the electrode material obtained in Example 1 and the polyacrylic acid binder in a mass ratio of 70:10:20. An evaluation cell of Example 3 was produced in the same manner as in [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 metallic 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 the 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 the 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 the polyacrylic acid binder was 40:40:20.

The obtained evaluation cell was subjected to a charge/discharge test in a constant temperature bath set at 25°C. The 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 constant current (CC) discharge and the discharge end potential was 1.2 V (vs. Li ^/ Li ⁺ ). The constant current value for charging and discharging was 0.1 C with 1200 C as the theoretical capacity of metallic silicon, 4200 mAh/g. In each cycle, a rest time of 10 minutes was set after charging and discharging. This cycle was performed 10 times. For each evaluation cell, the initial utilization rate of silicon, the cumulative irreversible capacity resulting from SEI (Solid Electrolyte Interface) formation, and the cumulative irreversible capacity resulting from the isolation of silicon 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 metallic silicon powder, and then dividing by 4200 mAh/g which is the theoretical capacity of metallic silicon.

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

As shown in Table 2, in Examples 3 to 6, the total irreversible capacity was smaller than in Comparative Examples 4 to 6. This is because the cumulative irreversible capacity resulting from SEI formation is small. From this, it is understood that in Examples 3 to 6, the decomposition of the non-aqueous electrolyte is suppressed. In Examples 5 and 6, in comparison with Examples 3 and 4, the irreversible capacity was small and the initial utilization rate of silicon was high. Therefore, when the electrode material according to the present embodiment is used by being mixed with the 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 a personal computer, an electronic device such as a communication terminal, a non-aqueous electrolyte secondary battery used as a power source for an automobile, a negative electrode provided therein, a material thereof, and the like.

1 non-aqueous 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 electricity storage unit 30 electricity storage device

Claims (5)

Including a carbon material having an average pore diameter of 40 Å or less and a negative electrode active material,
A composite electrode material for a non-aqueous electrolyte secondary battery, wherein the content of the carbon material is 1% by mass or more and 50% by mass or less . The composite electrode material according to claim 1, wherein the BET specific surface area of the carbon material is 100 m ² /g or more and 3,000 m ² /g or less. A negative electrode for a non-aqueous electrolyte secondary battery, comprising a negative electrode active material layer containing the composite electrode material according to claim 1 or 2 . The negative electrode for a non-aqueous electrolyte secondary battery according to claim 3 , wherein the ratio 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 non-aqueous electrolyte secondary battery comprising the negative electrode according to claim 3 or 4 .

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