JP6958272B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery according to the present invention is used, for example, as a driving power source or an auxiliary power source for a motor of a vehicle such as an electric vehicle, a fuel cell vehicle, or a hybrid electric vehicle.

In recent years, it has been required to reduce the amount of carbon dioxide in order to cope with global warming. Therefore, non-aqueous electrolyte secondary batteries having a low environmental load are being used not only for portable devices and the like, but also for power supply devices for electric vehicles such as hybrid vehicles (HEV), electric vehicles (EV), and fuel cell vehicles. .. Lithium-ion secondary batteries intended for application to electric vehicles are required to have a large capacity and a large area to have a high capacity.

Conventionally, a carbon material such as graphite, which is advantageous in terms of charge / discharge cycle life and cost, has been used for the negative electrode of a lithium ion secondary battery. However, in a negative electrode active material using a carbon material such as graphite, charging and discharging are performed by occluding and discharging lithium ions into graphite crystals, so the _{theoretical capacity obtained from LiC 6} , which is the maximum lithium-introduced compound, is 372 mAh / g or more. There is a drawback that the charge / discharge capacity of graphite cannot be obtained. For this reason, it is difficult to obtain a capacity and energy density that satisfy the practical level for vehicle applications only with a negative electrode active material using a carbon material such as graphite.

On the other hand, a battery using a material that alloys with Li as the negative electrode active material has an improved energy density as compared with a conventional battery using a carbon material such as graphite, and is therefore expected as a negative electrode active material for vehicle applications. Has been done. _{For example, the Si material occludes and releases 3.75} mol of lithium ions per mol during charging and discharging, and has a theoretical capacity of 3600 mAh / g for _{Li 15} Si ₄ (= Li 3.75 Si).

However, a lithium ion secondary battery using a material that alloys Li with Li for the negative electrode, particularly a Si material, has a large expansion and contraction at the negative electrode during charging and discharging. For example, the volume expansion when Li ions are occluded is about 1.2 times in the graphite material, whereas in the Si material, when Si and Li are alloyed, the volume expands from the amorphous state to the crystalline state and is about 4 times. There is a problem that the cycle life of the electrode is shortened because a large volume change is caused. Further, in the case of the Si negative electrode active material, there is a trade-off relationship between the capacity and the cycle durability, and there is a problem that it is difficult to improve the high cycle durability while exhibiting a high capacity.

In order to solve these problems, _{in a negative electrode in which SiO x} (0.5 ≦ x ≦ 1.5) having a structure in which _{ultrafine particles of Si are dispersed in SiO 2} is used in combination with graphite as a negative electrode active material, SiO _{x A technique for controlling the content ratio of SiO x} negative electrode active material to the total content of the negative electrode active material and graphite to a value in the range of 3 to 20% by mass has been proposed (see, for example, Patent Document 1). _{According to this technology, while using SiO x} having a high capacity and a large volume change due to charge / discharge, it is possible to suppress a decrease in battery characteristics due to the volume change, and as a result, a decrease in cycle durability is prevented. It is said that it can be done.

Japanese Unexamined Patent Publication No. 2012-89521

According to the studies by the present inventors, it has been confirmed that it is possible to suppress the decrease in the cycle durability of the battery to some extent according to the technique described in Patent Document 1. However, it has been found that this technique has a problem that a sufficient value cannot be secured as the initial discharge capacity (energy density). As described above, if the initial discharge capacity (energy density) is not sufficiently obtained, the meaning of using a high-capacity negative electrode active material such as _{SiO x is lost.}

Therefore, according to the present invention, in a non-aqueous electrolyte secondary battery in which a Si material and a carbon material are mixed and used as a negative electrode active material, the initial discharge capacity (energy density) is sufficiently secured and the cycle durability is lowered. The purpose is to provide a means that can suppress the energy.

The present inventors have conducted diligent research in order to solve the above problems. As a result, a Si-containing alloy is used as the Si material among the negative electrode active materials, used in combination with a predetermined carbon material having a Young's modulus of a predetermined value or more, and the content ratio of the carbon material is controlled to a value within a predetermined range. By doing so, it was found that the above problems could be solved, and the present invention was completed.

That is, the present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery having a current collector and a negative electrode active material layer containing a negative electrode active material arranged on the surface of the current collector. The negative electrode active material is selected from the group consisting of a Si-containing alloy, graphite, non-graphitized carbon, and amorphous carbon, and has a Young's modulus of 30 GPa or more measured by the measuring method specified in JIS R 7222-1997. Including carbon materials that are. The carbon material content in the total content of the Si-containing alloy and the carbon material is 5 to 15% by mass.

According to the present invention, in a non-aqueous electrolyte secondary battery in which a Si material and a carbon material are mixed and used as a negative electrode active material, the initial discharge capacity (energy density) is sufficiently secured and the cycle durability is lowered. Can also be suppressed.

It is sectional drawing which shows the basic structure of the flat type (laminated type) non-bipolar type lithium ion secondary battery which is one Embodiment of the non-aqueous electrolyte secondary battery which concerns on this invention. It is a perspective view which showed the appearance of the flat lithium ion secondary battery which is a typical embodiment of the non-aqueous electrolyte secondary battery which concerns on this invention.

According to one embodiment of the present invention, the negative electrode for a non-aqueous electrolyte secondary battery having a current collector and a negative electrode active material layer containing a negative electrode active material arranged on the surface of the current collector. The negative electrode active material is selected from the group consisting of Si-containing alloy, graphite, non-graphitized carbon, and amorphous carbon, and the Young rate measured by the measuring method specified in JIS R 7222-1997 is 30 GPa or more. Provided is a negative electrode for a non-aqueous electrolyte secondary battery, which comprises a material, and the content ratio of the carbon material in the total content of the Si-containing alloy and the carbon material is 5 to 15% by mass. Will be done.

In recent years, electric vehicles have been attracting attention as being environmentally friendly, but their cruising range is shorter than that of gasoline-powered vehicles, and the short cruising range is particularly remarkable when using air conditioning (cooling, heating). For this reason, non-aqueous electrolyte secondary batteries, particularly non-aqueous electrolyte secondary batteries for electric vehicles, are required to have high output and high capacity in order to extend the cruising range in one charge. In addition, improving durability (cycle characteristics) is an important issue for batteries mounted on electric vehicles so that high output and high capacity do not deteriorate even with repeated charging and discharging at a large current for a short time. ..

As described above, the present inventors use a material having a Young's modulus of a predetermined value or more as the carbon material in the combined system of the Si-containing alloy and the carbon material at a predetermined ratio, thereby performing the initial discharge capacity (energy). It has been found that it is possible to suppress a decrease in cycle durability while ensuring a sufficient density).

Hereinafter, an embodiment of the present invention (a lithium ion secondary battery to which a negative electrode for a non-aqueous electrolyte secondary battery according to the present embodiment is applied) will be described with reference to the attached drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios.

[Non-aqueous electrolyte secondary battery]
FIG. 1 is a schematic cross-sectional view schematically showing an outline of a flat laminated battery according to an embodiment of the battery of the present invention. By making it a laminated type, the battery can be made compact and has a high capacity. In this specification, the flat laminated non-bipolar lithium ion secondary battery shown in FIG. 1 will be described in detail as an example.

When viewed in terms of the electrical connection form (electrode structure) inside the lithium-ion secondary battery, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries. Is.

When distinguished by the type of electrolyte layer in the lithium ion secondary battery, a solution electrolyte type battery using a solution electrolyte such as a non-aqueous electrolyte solution for the electrolyte layer, a polymer battery using a polymer electrolyte for the electrolyte layer, etc. It can be applied to any conventionally known type of electrolyte layer. The polymer battery is further divided into a gel electrolyte type battery using a polymer gel electrolyte (also simply referred to as a gel electrolyte) and a solid polymer (all solid) type battery using a polymer solid electrolyte (also simply referred to as a polymer electrolyte). Be done.

Therefore, in the following description, as an example of the lithium ion secondary battery of the present embodiment, a non-bipolar type (internal parallel connection type) lithium ion secondary battery will be described very briefly with reference to the drawings. However, the technical scope of the electric device according to the present invention and the lithium ion secondary battery according to the present embodiment should not be limited to these.

FIG. 1 is a schematic cross-sectional view schematically showing the basic configuration of a flat laminated non-bipolar non-aqueous electrolyte lithium ion secondary battery (hereinafter, also simply referred to as “laminated battery”). As shown in FIG. 1, the laminated battery 10 of the present embodiment has a structure in which a flat, substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a battery exterior material 29 which is an exterior body. Has. Here, the power generation element 21 has a configuration in which a positive electrode, a separator 17, and a negative electrode are laminated. The separator 17 contains a non-aqueous electrolyte (for example, a liquid electrolyte). The positive electrode has a structure in which the positive electrode active material layers 15 are arranged on both sides of the positive electrode current collector 12. The negative electrode has a structure in which the negative electrode active material layers 13 are arranged on both sides of the negative electrode current collector 11. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 15 and the negative electrode active material layer 13 adjacent thereto face each other with the separator 17 interposed therebetween. As a result, the adjacent positive electrode, electrolyte layer and negative electrode form one cell cell layer 19. Therefore, it can be said that the laminated battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are laminated and electrically connected in parallel.

Although the negative electrode active material layer 13 is arranged on only one side of each of the outermost layer negative electrode current collectors located in both outermost layers of the power generation element 21, active material layers may be provided on both sides. That is, instead of using a current collector dedicated to the outermost layer in which the active material layer is provided on only one side, a current collector having active material layers on both sides may be used as it is as the current collector in the outermost layer. Further, by reversing the arrangement of the positive electrode and the negative electrode as in FIG. 1, the outermost layer positive electrode current collectors are located on both outermost layers of the power generation element 21, and the outermost layer positive electrode current collectors are placed on one side or both sides of the outermost layer positive electrode current collectors. The positive electrode active material layer may be arranged.

A positive electrode current collector plate (tab) 27 and a negative electrode current collector plate (tab) 25 that are conductive to each electrode (positive electrode and negative electrode) are attached to the positive electrode current collector 12 and the negative electrode current collector 11, respectively, and the battery exterior material 29 It has a structure that is led out to the outside of the battery exterior material 29 so as to be sandwiched between the ends of the battery. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 are ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode via positive electrode leads and negative electrode leads (not shown), respectively, as necessary. It may be attached by resistance welding or the like.

Hereinafter, the main components of the battery will be described.

<Active material layer>
The active material layer (13, 15) contains the active material and, if necessary, further contains other additives.

[Positive electrode active material layer]
The positive electrode active material layer 15 contains a positive electrode active material, and if necessary, a binder, a conductive auxiliary agent, an electrolyte (polymer matrix, an ionic conductive polymer, an electrolytic solution, etc.), a lithium salt for enhancing ionic conductivity, and the like. Further contains other additives of.

(Positive electrode active material)
Examples of the positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni-Mn-Co) O _2, and lithium such as those in which some of these transition metals are replaced by other elements. Examples thereof include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. In some cases, two or more kinds of positive electrode active materials may be used in combination.

More preferably, Li (Ni-Mn-Co) O ₂ and a part of these transition metals substituted with other elements (hereinafter, also simply referred to as "NMC composite oxide") are used. The NMC composite oxide has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are arranged in an orderly manner) atomic layer are alternately stacked via an oxygen atomic layer. Further, one Li atom is contained in each atom of the transition metal, and the amount of Li that can be taken out is twice that of the spinel-based lithium manganese oxide, that is, the supply capacity is doubled, and a high capacity can be obtained.

As described above, the NMC composite oxide also includes a composite oxide in which a part of the transition metal element is replaced with another metal element. Other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu. , Ag, Zn and the like. Preferred are Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr. More preferably, it is Ti, Zr, P, Al, Mg, Cr. From the viewpoint of improving the cycle characteristics, Ti, Zr, Al, Mg and Cr are more preferable.

NMC composite oxide, since the theoretical discharge capacity is high, preferably the general formula _{(1): Li a Ni b} Mn c Co d M x O 2 ( In the formula, a, b, c, d, x Satisfies 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3. M is Ti, Zr, It has a composition represented by (at least one selected from Nb, W, P, Al, Mg, V, Ca, Sr and Cr). Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents. In the above general formula (1), the relationship between b, c and d is not particularly limited and varies depending on the valence of M and the like, but it is preferable that b + c + d = 1 is satisfied. The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

In general, nickel (Ni), cobalt (Co) and manganese (Mn) are known to contribute to capacitance and output characteristics from the viewpoint of improving material purity and electron conductivity. Ti and the like partially replace the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, some of the transition elements may be replaced by other metal elements. In this case, it is preferable that 0 <x ≦ 0.3 in the general formula (1). The crystal structure is stabilized by solid solution of at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr, resulting in charging and discharging. It is considered that the battery capacity can be prevented from decreasing even if the above steps are repeated, and excellent cycle characteristics can be realized.

The NMC composite oxide can be prepared by selecting various known methods such as a coprecipitation method and a spray-drying method. Since the composite oxide can be easily prepared, it is preferable to use the coprecipitation method. Specifically, for example, as in the method described in Japanese Patent Application Laid-Open No. 2011-105588, a nickel-cobalt-manganese composite hydroxide is produced by a coprecipitation method. Then, the nickel-cobalt-manganese composite hydroxide and the lithium compound are mixed and calcined to obtain an NMC composite oxide.

Needless to say, a positive electrode active material other than the above may be used.

The average particle size of the positive electrode active material contained in the positive electrode active material layer is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 25 μm from the viewpoint of increasing the output. In this specification, the average particle size adopts the value of D50 measured by the particle size distribution measuring device of the laser diffraction / scattering method.

The content of the positive electrode active material (in terms of solid content) in the positive electrode active material layer is preferably 80 to 99.5% by mass, more preferably 85 to 99.5% by mass.

The density of the positive electrode active material layer is preferably 2.5 to 3.8 g / cm ³ and more preferably ^{2.6 to 3.7 g / cm 3 from the viewpoint of increasing the density.}

The single-side coating amount (base weight) of the positive electrode active material layer is preferably 12 to 30 mg / cm ² and more preferably ^{15 to 28 mg / cm 2 from the viewpoint of increasing the volume.}

(Binder)
The binder used for the positive electrode active material layer is not particularly limited, and examples thereof include the following materials. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile, polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC) and its salts, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR) ), Isoprene rubber, butadiene rubber, ethylene-propylene rubber, ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and its hydrogen additive, styrene / isoprene / styrene block copolymer and its hydrogen addition Thermoplastic polymers such as fluoropolymers, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA) ), Fluororesin such as ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinylfluorovinyl (PVF), vinylidene fluoride -Hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluororubber), vinylidene fluoride-pentafluoropropylene-based fluoropolymer Rubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluororubber (VDF-PFMVE-TFE-based fluororubber), vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber) and other vinylidene fluoride-based fluororubbers, epoxy resins and the like can be mentioned. These binders may be used alone or in combination of two or more.

The binder content in the positive electrode active material layer is preferably 1 to 10% by mass, more preferably 1 to 8% by mass.

(Conductive aid)
The conductive additive refers to an additive added to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Various conductive auxiliaries include carbon blacks such as acetylene black, Ketjen black (registered trademark) and furnace black, carbon powders such as channel black and thermal black, and vapor-grown carbon fibers (VGCF; registered trademark). Examples include carbon materials such as carbon fiber. When the active material layer contains a conductive auxiliary agent, an electronic network inside the active material layer is effectively formed, which can contribute to the improvement of the output characteristics of the battery.

The content of the conductive auxiliary agent in the positive electrode active material layer is preferably 1 to 10% by mass, and more preferably 1 to 8% by mass. The following effects are exhibited by defining the blending ratio (content) of the conductive auxiliary agent within the above range. That is, the electron conductivity can be sufficiently ensured without inhibiting the electrode reaction, the decrease in energy density due to the decrease in electrode density can be suppressed, and the energy density can be improved by improving the electrode density. It is.

(Other ingredients)
Examples of the lithium salt include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF _{6 , LiBF 4} , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

Examples of the ionic conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

The compounding ratio of the components contained in the positive electrode active material layer is not particularly limited. The compounding ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

The positive electrode (positive electrode active material layer) can be coated by any of a kneading method, a sputtering method, a vapor deposition method, a CVD method, a PVD method, an ion plating method, and a thermal spraying method, in addition to a normal slurry coating method. Can be formed.

The porosity of the positive electrode active material layer is in the range of 10 to 45% by volume, preferably 15 to 40% by volume, and more preferably 20 to 35% by volume with respect to the total volume of the positive electrode active material layer. When the pore ratio is within the above range, the pores of the active material layer are impregnated with the electrolytic solution even inside the active material layer without impairing the characteristics and strength such as battery capacity, so that the electrode reaction is promoted. This is because it can effectively function as a pathway for supplying the electrolytic solution (Li ^{+ ion) to the battery.}

The thickness of the positive electrode active material layer (active material layer on one side of the current collector) is also not particularly limited, and conventionally known knowledge about the battery can be appropriately referred to. As an example, the thickness of the positive electrode active material layer is usually about 1 to 500 μm, preferably about 50 to 100 μm, in consideration of the purpose of use of the battery (emphasis on output, emphasis on energy, etc.) and ionic conductivity.

[Negative electrode active material layer]
In the non-aqueous electrolyte secondary battery according to the present embodiment, the negative electrode active material layer 13 contains a negative electrode active material.

The negative electrode active material contained in the negative electrode active material layer 13 indispensably contains a Si-containing alloy and a predetermined carbon material.

(Si-containing alloy)
One of the negative electrode active materials essentially contained in the negative electrode active material layer 13 is a Si-containing alloy.

The Si-containing alloy is not particularly limited as long as it is an alloy with another metal containing Si, and conventionally known findings can be appropriately referred to. Here, as a preferred embodiment of the Si-containing _{alloy, Si x Ti y Ge z A} a, Si x Ti y Zn z A a, Si x Ti y Sn z A a, Si x Sn y Al z A a, Si x Sn _y V _z A _a , Si _x Sn _y C _z A _a , Si _x Zn _y V _z A _a , Si _x Zn _y Sn _z A _a , Si _x Zn _y Al _z A _a , Si _x Zn _y C _z A _{a, Si x Al y C z} a a and _{Si x Al y Nb z a a} ( wherein, a is unavoidable impurities. further, x, y, z, and a represent the value of mass%, 0 <x <100, 0 <y <100, 0 ≦ z <100, and 0 ≦ a <0.5, and x + y + z + a = 100). More preferably, it is a Si-containing alloy that further satisfies 0 <z <100 in the above formula. By using these Si-containing alloys as the negative electrode active material, the phase transition of amorphous-crystal is suppressed during Li alloying by appropriately selecting the predetermined first additive element and the predetermined second additive element. Therefore, the cycle life can be improved. Further, this makes the capacity of the conventional negative electrode active material higher than that of the conventional negative electrode active material, for example, a carbon-based negative electrode active material. Among them, from the viewpoint of capacity and cycle life, a Si—Ti alloy containing Ti in addition to Si is preferably used, and a Si—Sn—Ti alloy containing Sn is more preferably used.

The average particle size of the Si-containing alloy is not particularly limited. From the viewpoint of increasing the output, the secondary particle size D50 is preferably in the range of 1 to 20 μm, and more preferably D50 is in the range of 2 to 10 μm. Further, preferably, the secondary particle size D90 is in the range of 5 to 100 μm. Here, the value obtained by the laser diffraction method is used as the secondary particle size of the Si material. However, it goes without saying that the range is not limited to the above range and may be outside the above range as long as the effects of the present embodiment can be effectively exhibited. The shape of the Si-containing alloy is not particularly limited, and may be spherical, elliptical, columnar, polygonal, scaly, amorphous, or the like.

Method for Producing Si-Containing Alloy The method for producing the Si-containing alloy according to this embodiment is not particularly limited, and can be produced by using various conventionally known production methods. Examples of the manufacturing method of the Si-containing alloy include the following manufacturing methods, but the manufacturing method is not limited thereto.

First, a step of mixing the raw materials of the Si-containing alloy to obtain a mixed powder is performed. In this step, the raw materials of the alloy are mixed in consideration of the composition of the obtained Si-containing alloy. As the raw material of the alloy, the form thereof is not particularly limited as long as the ratio of the elements required for the Si-containing alloy can be realized. For example, a simple substance constituting a Si-containing alloy may be mixed in a target ratio, or an alloy, a solid solution, or an intermetallic compound having a target element ratio can be used. In addition, the raw materials in a powder state are usually mixed. As a result, a mixed powder made of raw materials is obtained.

Subsequently, the mixed powder obtained above is alloyed. As a result, a Si-containing alloy that can be used as a negative electrode active material for a non-aqueous electrolyte secondary battery can be obtained.

The alloying method includes a solid phase method, a liquid phase method, and a gas phase method. For example, a mechanical alloy method, an arc plasma melting method, a casting method, a gas atomizing method, a liquid quenching method, an ion beam sputtering method, and a vacuum method. Examples include a vapor deposition method, a plating method, and a vapor phase chemical reaction method. Above all, it is preferable to perform the alloying treatment by using the mechanical alloy method. It is preferable to perform the alloying treatment by the mechanical alloy method because the phase state can be easily controlled. Further, a step of melting the raw material and a step of quenching and solidifying the melted melt may be included before performing the alloying treatment.

The alloying treatment by the above-mentioned method is usually performed in a dry atmosphere, but the particle size distribution after the alloying treatment may have a very large or small range. Therefore, it is preferable to perform a pulverization treatment and / or a classification treatment for adjusting the particle size.

The particle size of the particles obtained by the alloying treatment can be controlled by appropriately performing treatments such as classification and pulverization. Examples of the classification method include wind power classification, mesh filtration method, and sedimentation method. Further, the crushing conditions are not particularly limited, and the crushing time, rotation speed, etc. by an appropriate crusher (for example, a device that can also be used by the mechanical alloy method, for example, a planetary ball mill) may be appropriately set. As an example of the crushing conditions, there is an example in which crushing is performed at a rotation speed of 200 to 400 rpm for 30 minutes to 4 hours using a crusher such as a planetary ball mill.

(Carbon material)
The other negative electrode active material essentially contained in the negative electrode active material layer 13 is selected from the group consisting of graphite, non-graphitized carbon, and amorphous carbon, and is measured by the measuring method specified in JIS R 7222-1997. It is a carbon material having a young rate of 30 GPa or more.

As described above, the type of carbon material is one or more selected from the group consisting of graphite, non-graphitized carbon, and amorphous carbon. Specifically, graphite (graphite), which is a highly crystalline carbon such as natural graphite and artificial graphite; non-graphitized carbon such as hard carbon; and Ketjen Black (registered trademark), acetylene black, channel black, lamp black, and oil furnace. One or more selected from amorphous carbon such as carbon black such as black and thermal black. Of these, it is preferable to use graphite such as natural graphite or artificial graphite.

The average particle size (D50) of the carbon material is also not particularly limited. Again, from the viewpoint of high output, it is preferably 5 to 40 μm, and more preferably 10 to 30 μm. Further, from the viewpoint of further improving the cycle durability, the average particle size (D50) of the carbon material is preferably larger than the average particle size (D50) of the Si-containing alloy. The shape of the carbon material is not particularly limited and may be spherical, elliptical, cylindrical, polygonal, scaly, amorphous or the like. The value of the BET specific surface area of the carbon material is also not particularly limited, but is preferably 50 m ² / g or less, more preferably 20 m ² / g or less (the lower limit is not particularly limited, but for example, 1 m ^2). / G or more).

Further, the value of Young's modulus (tensile elastic modulus) of the carbon material is indispensably 30 GPa or more. When a carbon material with a low Young's modulus is used and used in combination with a Si-containing alloy, it is possible to secure a sufficient initial discharge capacity (energy density), but it is possible to sufficiently suppress a decrease in cycle durability. There is a problem that it cannot be done. On the other hand, by using the above-mentioned predetermined carbon material having a Young's modulus as large as 30 GPa or more in combination with the Si-containing alloy, the initial discharge capacity (energy density) is sufficiently secured and the decrease in cycle durability is prevented. It becomes possible to do.

Here, the value of Young's modulus of the carbon material is measured by the measuring method specified in JIS R 7222-1997. The upper limit of the Young's modulus of the carbon material is not particularly limited, but is preferably 40 GPa or less. Since the Young's modulus differs depending on the structure and apparent density of the carbon material, it is possible to select carbon materials having Young's modulus within / outside the above range by appropriately selecting the type and structure of the carbon material. It is possible. As an example, the Young's modulus tends to increase when the apparent density of the carbon material is small. Further, even when the same production raw material is used, the Young's modulus of the obtained carbon material is still different if the production conditions of the carbon material are different. Therefore, it is possible to select carbon materials having Young's modulus within / outside the above range by appropriately setting the production conditions such as the heat treatment temperature and the heat treatment time at the time of producing the carbon material. As an example, the Young's modulus tends to increase as the temperature during the heat treatment increases (however, the Young's modulus decreases when the temperature becomes too high).

In the non-aqueous electrolyte secondary battery according to this embodiment, the range of the content ratio of the Si-containing alloy and the carbon material described above is defined. Specifically, it is essential that the content ratio of the carbon material in the total content of the Si-containing alloy and the carbon material is 5 to 15% by mass. Here, if the content ratio of the carbon material to the total content is too small, the initial discharge capacity (energy density) is improved, but there is a problem that the cycle durability is remarkably lowered. Further, if the content ratio is too large, the initial discharge capacity (energy density) is lowered, and there is a problem that the significance of using the Si-containing alloy is impaired in the first place. On the other hand, by controlling the content ratio in the range of 5 to 15% by mass, both the initial capacity (energy density) and the cycle durability are achieved, and the secondary non-aqueous electrolyte has a well-balanced performance. Batteries may be provided.

The mechanism by which such effects occur has not been completely clarified, but the following mechanisms have been presumed. That is, in a negative electrode having no configuration according to the present embodiment (a negative electrode containing only a Si-containing alloy as a negative electrode active material, or a negative electrode containing a carbon material but having a small young ratio), the Si-containing alloy shrinks during discharge. As a result, voids are formed between the particles of the negative electrode active material, and as a result, the conductive path in the negative electrode active material layer is cut. Therefore, the internal resistance of the battery in the negative electrode active material layer increases, and the cycle durability decreases. On the other hand, in the negative electrode active material layer of the negative electrode according to the present embodiment, when the Si-containing alloy expands during charging, the carbon material having a high Young's modulus is crushed. Since the crushed carbon material returns to its original shape due to elastic deformation during discharge, it is possible to maintain the same conductive bath as before charging / discharging. As a result, it is considered possible to suppress a decrease in cycle durability. Even if a carbon material having a small Young's modulus is used in combination with a Si-containing alloy, such an effect cannot be obtained because the carbon material collapses due to the compressive force accompanying the expansion of the Si-containing alloy during charging. It should be noted that this mechanism is based on speculation, and its correctness does not affect the technical scope of the present invention.

In some cases, a negative electrode active material other than the above-mentioned two types of negative electrode active materials may be used in combination. Examples of the negative electrode active material that can be used in combination include a lithium-transition metal composite oxide (for example, Li ₄ Ti ₅ O ₁₂ ), a metal material, a lithium alloy negative electrode material, _{and a mixture of amorphous SiO 2} particles and Si particles. A certain SiO _x (x represents the number of oxygen satisfying the valence of Si) and the like can be mentioned. Of course, other negative electrode active materials may be used. However, from the viewpoint of fully exhibiting the effects of the present invention, the total content of the above-mentioned two types of negative electrode active materials (Si-containing alloy and carbon material having a predetermined Young ratio) is added to the negative electrode active material layer 13. It is preferably 50% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and 95% by mass or more, based on 100% by mass of the total amount of the negative electrode active material contained. Is more preferable, 98% by mass or more is particularly preferable, and 100% by mass is most preferable.

(Binder)
In the present embodiment, the negative electrode active material layer preferably contains a binder. Specific forms of the binder contained in the negative electrode active material layer include the above-mentioned materials as the binder contained in the positive electrode active material layer. It is also preferable that the negative electrode active material layer contains an aqueous binder. In addition to being easy to procure water as a raw material for water-based binders, since water vapor is generated during drying, capital investment in the production line can be significantly reduced, and the environmental load can be reduced. There is an advantage.

The aqueous binder refers to a binder using water as a solvent or a dispersion medium, and specifically, a thermoplastic resin, a polymer having rubber elasticity, a water-soluble polymer, or a mixture thereof. Here, the binder using water as a dispersion medium includes all expressed as latex or emulsion, and refers to a polymer emulsified or suspended in water, for example, a polymer latex emulsified and polymerized in a self-emulsifying system. Kind.

The water-based binder is at least one rubber-based binder selected from the group consisting of styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, and methyl methacrylate rubber from the viewpoint of binding properties. It is preferable to include it. Further, the water-based binder preferably contains styrene-butadiene rubber (SBR) because of its good binding property.

When styrene-butadiene rubber (SBR) suitable as an aqueous binder is used, it is preferable to use the following thickeners in combination from the viewpoint of improving coatability. Suitable thickeners to be used in combination with styrene-butadiene rubber (SBR) include polyvinyl alcohol and its modified products, starch and its modified products, cellulose derivatives (carboxymethyl cellulose (CMC), methyl cellulose, hydroxyethyl cellulose, and these. (Salt, etc.), polyvinylpyrrolidone, polyacrylic acid (salt), or polyethylene glycol. Above all, it is preferable to combine styrene-butadiene rubber (SBR) with carboxymethyl cellulose (CMC) or a salt thereof (CMC (salt)). The mass ratio of SBR (water-based binder) and the thickener is not particularly limited, but SBR (water-based binder): thickener = 1: (0.3 to 0.7). Is preferable.

The amount of binder contained in the negative electrode active material layer is not particularly limited as long as it can bind the active material, but is preferably 0 with respect to 100% by mass of the total amount of the negative electrode active material layer. It is 5 to 15% by mass, more preferably 1 to 10% by mass, further preferably 1 to 8% by mass, particularly preferably 1 to 4% by mass, and most preferably 1.5 to 3%. It is 5.5% by mass. Since the water-based binder has a high binding force, the active material layer can be formed by adding a small amount as compared with the organic solvent-based binder.

In a preferred embodiment of the present embodiment, the negative electrode active material layer preferably contains polyimide or SBR as a binder, and particularly preferably contains polyimide. It is preferable that the negative electrode active material layer contains polyimide as a binder because the effects of the present invention are further exhibited.

In addition to the negative electrode active material and the binder, the negative electrode active material layer includes, if necessary, a conductive additive, an electrolyte (polymer matrix, ionic conductive polymer, electrolytic solution, etc.), and ionic conductivity in addition to the above-mentioned thickener. Further contains other additives such as lithium salts to enhance. Unless otherwise specified herein, these specific forms are the same as those of the positive electrode active material layer.

The content of the conductive auxiliary agent in the negative electrode active material layer is preferably 0.1 to 10% by mass, and more preferably 0.5 to 8% by mass. The following effects are exhibited by defining the blending ratio (content) of the conductive auxiliary agent within the above range. That is, the electron conductivity can be sufficiently ensured without inhibiting the electrode reaction, the decrease in energy density due to the decrease in electrode density can be suppressed, and the energy density can be improved by improving the electrode density. It is.

The compounding ratio of the components contained in the negative electrode active material layer is not particularly limited. The compounding ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

The porosity of the negative electrode active material layer is in the range of 10 to 45% by volume, preferably 15 to 40% by volume, and more preferably 20 to 35% by volume with respect to the total volume of the negative electrode active material layer. When the pore ratio is within the above range, the pores of the active material layer are impregnated with the electrolytic solution even inside the active material layer without impairing the characteristics and strength such as battery capacity, so that the electrode reaction is promoted. This is because it can effectively function as a pathway for supplying the electrolytic solution (Li ^{+ ion) to the battery.}

In the present embodiment, the density of the negative electrode active material layer is not particularly limited ^{, but is preferably 1.5 to 1.8 g / cm 3} from the viewpoint of increasing the density, and is preferably 1.5 to 1.7 g / cm. It is more preferably ^3.

Sided coating amount of the negative electrode active material layer (weight per unit area) is not particularly limited, is preferably from 5 to 20 mg / cm ^2, more preferably 8~15mg / cm ^2. When the amount of one-sided coating of the negative electrode active material layer is 20 mg / cm ² or less, the rate characteristics of the battery can be improved. On the other hand, if the amount of one-sided coating of the negative electrode active material layer is 5 mg / cm ² or more, a sufficient capacity can be secured.

The thickness of the negative active material layer (active material layer on one side of the current collector) is also not particularly limited, and conventionally known knowledge about the battery can be appropriately referred to. As an example, the thickness of the negative electrode active material layer is usually about 1 to 500 μm, preferably about 50 to 150 μm in consideration of the purpose of use of the battery (emphasis on output, emphasis on energy, etc.) and ionic conductivity.

The negative electrode active material layer can be formed by applying a negative electrode active material slurry containing a negative electrode active material, a binder, a conductive auxiliary agent, a solvent, etc. onto the current collector, but further when preparing the negative electrode active material slurry. A crushing treatment may be performed. The crushing means is not particularly limited, and known means can be appropriately adopted. The crushing conditions are not particularly limited, and the crushing time, rotation speed, and the like may be appropriately set. As an example of the crushing conditions, there is an example of crushing at a rotation speed of 200 to 400 rpm for 30 minutes to 4 hours. Further, the pulverization treatment may be carried out in several times with a cooling time in between, for the purpose of preventing the solvent from being heated and denatured by the pulverization treatment.

<Current collector>
The current collectors (11, 12) are made of a conductive material. The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires high energy density, a current collector having a large area is used.

There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm.

The shape of the current collector is also not particularly limited. In the laminated battery 10 shown in FIG. 1, in addition to the current collector foil, a mesh shape (expanded grid or the like) or the like can be used.

There are no particular restrictions on the materials that make up the current collector. For example, a metal or a resin obtained by adding a conductive filler to a conductive polymer material or a non-conductive polymer material can be adopted.

Specific examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Further, the foil may be a metal surface coated with aluminum. Of these, aluminum, stainless steel, copper, and nickel are preferable from the viewpoints of electron conductivity, battery operating potential, adhesion of the negative electrode active material by sputtering to the current collector, and the like.

Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

Examples of the non-conductive polymer material include polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), and polyimide. (PI), Polyethyleneimide (PAI), Polyethylene (PA), Polytetrafluoroethylene (PTFE), Styrene-butadiene rubber (SBR), Polyacrylonitrile (PAN), Polymethylacrylate (PMA), Polymethylmethacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), polystyrene (PS) and the like. Such non-conductive polymer materials can have excellent potential resistance or solvent resistance.

A conductive filler may be added to the above-mentioned conductive polymer material or non-conductive polymer material, if necessary. In particular, when the resin used as the base material of the current collector is composed of only a non-conductive polymer, a conductive filler is inevitably indispensable in order to impart conductivity to the resin.

The conductive filler can be used without particular limitation as long as it is a conductive substance. For example, materials having excellent conductivity, potential resistance, or lithium ion blocking property include metals and conductive carbon. The metal is not particularly limited, but is at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or a metal thereof. It is preferable to contain an alloy containing, or a metal oxide. Further, the conductive carbon is not particularly limited. Preferably, it is selected from the group consisting of acetylene black, vulcan (registered trademark), black pearl (registered trademark), carbon nanofiber, Ketjen black (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. It contains at least one species.

The amount of the conductive filler added is not particularly limited as long as it can impart sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

<Separator (electrolyte layer)>
The separator has a function of holding an electrolyte and ensuring lithium ion conductivity between the positive electrode and the negative electrode, and a function as a partition wall between the positive electrode and the negative electrode.

Examples of the form of the separator include a porous sheet separator made of a polymer or fiber that absorbs and retains the electrolyte, a non-woven fabric separator, and the like.

As the separator of the porous sheet made of polymer or fiber, for example, microporous (microporous membrane) can be used. Specific forms of the porous sheet made of the polymer or fiber include, for example, a polyolefin such as polyethylene (PE) and polypropylene (PP); a laminate in which a plurality of these are laminated (for example, three layers of PP / PE / PP). Examples thereof include a microporous (microporous film) separator made of a laminated body having a structure, etc.), a hydrocarbon resin such as polyethylene, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), and glass fiber.

The thickness of the microporous (microporous membrane) separator cannot be uniquely specified because it differs depending on the intended use. To give an example, in applications such as a secondary battery for driving a motor such as an electric vehicle (EV), a hybrid electric vehicle (HEV), and a fuel cell vehicle (FCV), the length is 4 to 60 μm in a single layer or a multilayer. Is desirable. It is desirable that the fine pore size of the microporous (microporous membrane) separator is 1 μm or less (usually, the pore size is about several tens of nm) at the maximum.

As the non-woven fabric separator, conventionally known ones such as cotton, rayon, acetate, nylon, polyester; polyolefin such as PP and PE; polyimide and aramid are used alone or in combination. Further, the bulk density of the non-woven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated electrolyte. Further, the thickness of the non-woven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, and particularly preferably 10 to 100 μm.

Also, as mentioned above, the separator contains an electrolyte. The electrolyte is not particularly limited as long as it can exhibit such a function, but a liquid electrolyte or a gel polymer electrolyte is used. By using the gel polymer electrolyte, the distance between the electrodes is stabilized, the occurrence of polarization is suppressed, and the durability (cycle characteristics) is improved.

The liquid electrolyte has a function as a carrier of lithium ions. The liquid electrolyte constituting the electrolytic solution layer has a form in which a lithium salt is dissolved in an organic solvent which is a plasticizer. Examples of the organic solvent used include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. As the lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiClO 4, LiAsF 6, LiTaF such 6, LiCF ₃ SO ₃ Compounds that can be added to the active material layer of the electrode can also be employed. The liquid electrolyte may further contain additives other than the above-mentioned components. Specific examples of such additives include, for example, vinylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate, phenylvinylene carbonate, diphenylvinylene carbonate, ethylvinylene carbonate, diethylvinylene carbonate, vinylethylene carbonate, 1,2-divinylethylene. Carbonate, 1-methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, vinylvinylene carbonate, allylethylene carbonate, Vinyloxymethylethylene carbonate, allyloxymethylethylene carbonate, acrylicoxymethylethylene carbonate, methacryloxymethylethylene carbonate, ethynylethylene carbonate, propargylethylene carbonate, ethynyloxymethylethylene carbonate, propargyloxyethylene carbonate, methyleneethylene carbonate, 1,1 -Dimethyl-2-methyleneethylene carbonate and the like. Of these, vinylene carbonate, methylvinylene carbonate and vinylethylene carbonate are preferable, and vinylene carbonate and vinylethylene carbonate are more preferable. Only one of these additives may be used alone, or two or more of these additives may be used in combination.

The gel polymer electrolyte has a structure in which the above liquid electrolyte is injected into a matrix polymer (host polymer) made of an ionic conductive polymer. By using a gel polymer electrolyte as the electrolyte, the fluidity of the electrolyte is lost, and it is excellent in that it becomes easy by blocking the ionic conductivity between the layers. Examples of the ionic conductive polymer used as the matrix polymer (host polymer) include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyvinylidene fluoride-hexafluoropropylene (polyvinylidene fluoride-hexafluoropropylene). PVdF-HEP), poly (methyl methacrylate (PMMA)) and copolymers thereof and the like.

The matrix polymer of the gel electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, a suitable polymerization initiator is used, and a polymerizable polymer for forming a polyelectrolyte (for example, PEO or PPO) is subjected to thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. It may be polymerized.

Further, the separator is preferably a separator in which a heat-resistant insulating layer is laminated on a porous substrate such as a porous sheet separator or a non-woven fabric separator (separator with a heat-resistant insulating layer). The heat-resistant insulating layer is a ceramic layer containing inorganic particles and a binder. As the separator with a heat-resistant insulating layer, a separator having a melting point or a thermal softening point of 150 ° C. or higher, preferably 200 ° C. or higher, having high heat resistance is used. By having the heat-resistant insulating layer, the internal stress of the separator, which increases when the temperature rises, is relaxed, so that the effect of suppressing heat shrinkage can be obtained. As a result, it is possible to prevent the induction of a short circuit between the electrodes of the battery, so that the battery configuration is less likely to cause performance deterioration due to a temperature rise. Further, by having the heat-resistant insulating layer, the mechanical strength of the separator with the heat-resistant insulating layer is improved, and the film breakage of the separator is less likely to occur. Further, due to the effect of suppressing heat shrinkage and high mechanical strength, the separator is less likely to curl in the battery manufacturing process.

The inorganic particles in the heat-resistant insulating layer contribute to the mechanical strength of the heat-resistant insulating layer and the effect of suppressing heat shrinkage. The material used as the inorganic particles is not particularly limited. Examples include silicon, aluminum, zirconium, titanium oxides (SiO ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ ), hydroxides, and nitrides, and composites thereof. These inorganic particles may be derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, and mica, or may be artificially produced. In addition, only one of these inorganic particles may be used alone, or two or more of these inorganic particles may be used in combination. Of these, from the viewpoint of cost, it is preferable to use _{silica (SiO 2} ) or alumina (Al ₂ O ₃ ), and it is more preferable to use _{alumina (Al 2} O _3).

The basis weight of the heat-resistant particles is not particularly limited, but is preferably 5 to ^{15 g / m 2.} Within this range, sufficient ionic conductivity can be obtained and heat resistance is maintained, which is preferable.

The binder in the heat-resistant insulating layer has a role of adhering the inorganic particles to each other and the inorganic particles and the porous substrate. The binder stably forms the heat-resistant insulating layer and prevents peeling between the porous substrate and the heat-resistant insulating layer.

The binder used for the heat-resistant insulating layer is not particularly limited, and is, for example, carboxymethyl cellulose (CMC), polyacrylonitrile, cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), isoprene rubber. , Butadiene rubber, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), methyl acrylate and the like can be used as binders. Of these, carboxymethyl cellulose (CMC), methyl acrylate, or polyvinylidene fluoride (PVdF) is preferably used. Only one of these compounds may be used alone, or two or more of these compounds may be used in combination.

The binder content in the heat-resistant insulating layer is preferably 2 to 20% by mass with respect to 100% by mass of the heat-resistant insulating layer. When the binder content is 2% by mass or more, the peel strength between the heat-resistant insulating layer and the porous substrate can be increased, and the vibration resistance of the separator can be improved. On the other hand, when the binder content is 20% by mass or less, the gaps between the inorganic particles are appropriately maintained, so that sufficient lithium ion conductivity can be ensured.

The heat shrinkage of the separator with a heat-resistant insulating layer is preferably 10% or less for both MD and TD after holding for 1 hour under the conditions of ^{150 ° C. and 2 gf / cm 2.} By using such a material having high heat resistance, it is possible to effectively prevent the separator from shrinking even when the amount of heat generated by the positive electrode increases and the internal temperature of the battery reaches 150 ° C. As a result, it is possible to prevent the induction of a short circuit between the electrodes of the battery, so that the battery configuration is less likely to cause performance deterioration due to a temperature rise.

<Current collector plate (tab)>
In a lithium ion secondary battery, a current collector plate (tab) electrically connected to a current collector is taken out of a laminate film as an exterior material for the purpose of taking out current to the outside of the battery.

The material constituting the current collector plate is not particularly limited, and a known highly conductive material conventionally used as a current collector plate for a lithium ion secondary battery can be used.

As the constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. The same material may be used or different materials may be used for the positive electrode current collector plate (positive electrode tab) and the negative electrode current collector plate (negative electrode tab).

<Positive terminal lead and negative electrode terminal lead>
As the material of the negative electrode and positive electrode terminal leads, the leads used in known laminated secondary batteries can be used. The part taken out from the battery exterior material is heat-insulating so that it does not come into contact with peripheral devices or wiring and cause an electric leakage, which affects the product (for example, automobile parts, especially electronic devices). It is preferable to cover with a heat-shrinkable tube or the like.

<Battery exterior>
As the battery exterior, a conventionally known metal can case can be used. In addition, the power generation element 21 may be packed by using the laminated film 29 as shown in FIG. 1 as the exterior material. The laminated film can be configured as, for example, a three-layer structure in which polypropylene, aluminum, and nylon are laminated in this order. By using such a laminated film, it is possible to easily open the exterior material, add the capacity recovery material, and reseal the exterior material. A laminated film is desirable from the viewpoint of high output and excellent cooling performance, and can be suitably used for batteries for large devices for EVs and HEVs. Further, since the group pressure applied to the power generation element from the outside can be easily adjusted and the thickness of the electrolytic solution layer can be easily adjusted, the exterior body is made of a laminated film containing aluminum (for example,). Aluminum laminated sheet bag) is more preferable. As the laminated film containing aluminum, an aluminum laminate fill or the like in which the above-mentioned polypropylene, aluminum, and nylon are laminated in this order can be used.

[Cell size]
FIG. 2 is a perspective view showing the appearance of a flat lithium ion secondary battery, which is a typical embodiment of the secondary battery. According to a preferred embodiment of the present invention, such as this lithium ion secondary battery, there is provided a flat laminated laminated battery having a structure in which the power generation element is enclosed in a battery outer body made of a laminated film containing aluminum. NS.

As shown in FIG. 2, the flat lithium ion secondary battery 50 has a rectangular flat shape, and positive electrode tabs 58 and negative electrode tabs 59 for extracting electric power are pulled out from both side portions thereof. There is. The power generation element 57 is wrapped by the battery exterior material 52 of the lithium ion secondary battery 50, and the periphery thereof is heat-sealed. The power generation element 57 is sealed with the positive electrode tab 58 and the negative electrode tab 59 pulled out to the outside. Has been done. Here, the power generation element 57 corresponds to the power generation element 21 of the lithium ion secondary battery 10 shown in FIG. 2 described above. The power generation element 57 is formed by stacking a plurality of single battery layers (single cells) 19 composed of a positive electrode (positive electrode active material layer) 15, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 13.

Further, the extraction of the tabs 58 and 59 shown in FIG. 2 is not particularly limited. The positive electrode tab 58 and the negative electrode tab 59 may be pulled out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of each and taken out from each side. It is not limited to.

In a general electric vehicle, the battery storage space is about 170 L. Since the cell and auxiliary equipment such as charge / discharge control equipment are stored in this space, the storage space efficiency of the normal cell is about 50%. The loading efficiency of cells in this space is a factor that controls the cruising range of electric vehicles. If the size of the single cell becomes small, the loading efficiency is impaired, so that the cruising range cannot be secured.

Therefore, in the present invention, it is preferable that the battery structure in which the power generation element is covered with the exterior body is large. Specifically, it is preferable that the negative electrode active material layer has a rectangular shape (rectangular shape) and the length of the short side of the rectangle is 100 mm or more. Such large batteries can be used in vehicle applications. Here, the length of the short side of the negative electrode active material layer refers to the side having the shortest length among the electrodes. The upper limit of the length of the short side is not particularly limited, but is usually 400 mm or less.

The aspect ratio of the rectangular electrode is preferably 1 to 3, more preferably 1 to 2. The aspect ratio of the electrode is defined as the aspect ratio of the rectangular positive electrode active material layer. By setting the aspect ratio in such a range, there is an advantage that both vehicle required performance and mounting space can be achieved.

[Battery set]
An assembled battery is formed by connecting a plurality of batteries. More specifically, it is composed of serialization, parallelization, or both by using at least two or more. By serializing and parallelizing, the capacitance and voltage can be adjusted freely.

It is also possible to connect a plurality of batteries in series or in parallel to form a small assembled battery that can be attached / detached. Then, by connecting a plurality of these detachable small assembled batteries in series or in parallel, a large capacity and a large capacity suitable for a vehicle driving power source or an auxiliary power source that require a high volume energy density and a high volume output density. It is also possible to form an assembled battery having an output. How many batteries are connected to make an assembled battery, and how many stages of small assembled batteries are stacked to make a large-capacity assembled battery depends on the battery capacity of the vehicle (electric vehicle) to be installed. It may be decided according to the output.

[vehicle]
The non-aqueous electrolyte secondary battery of the present embodiment has excellent rate characteristics, maintains the discharge capacity even after long-term use, and has good cycle characteristics. In vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles, higher capacity and larger size are required and longer life is required compared to electric and portable electronic device applications. .. Therefore, the non-aqueous electrolyte secondary battery can be suitably used as a power source for a vehicle, for example, a vehicle drive power source or an auxiliary power source.

Specifically, a battery or an assembled battery formed by combining a plurality of batteries can be mounted on the vehicle. In the present embodiment, a long-life battery having excellent long-term reliability and output characteristics can be configured. Therefore, when such a battery is installed, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long one-charge mileage is configured. can. In addition to hybrid vehicles, fuel cell vehicles, electric vehicles (all four-wheeled vehicles (commercial vehicles such as passenger cars, trucks, buses, light vehicles, etc.)) This is because it becomes a highly reliable automobile with a long life by using it for two-wheeled vehicles (including motorcycles) and three-wheeled vehicles. However, the application is not limited to automobiles, and can be applied to various power sources of other vehicles, for example, moving objects such as trains, and power supplies for mounting such as uninterruptible power supplies. It is also possible to use it as.

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

1. 1. _{Preparation of positive electrode NMC composite oxide (average particle size D50: 15 μm) with a composition of LiNi 0.5} Mn _0.3 Co _0.2 O ₂ as a positive electrode active material 94% by mass, acetylene black 3% by mass as a conductive auxiliary agent, And as a binder, a solid content consisting of 3% by mass of polyvinylidene fluoride (PVdF) was prepared. The PVdF includes Kureha Battery Materials Japan Co., Ltd., Kureha KF polymer, powder type, grade No. W # 7200 was used. An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was mixed with this solid content to prepare a positive electrode active material slurry. The obtained positive electrode active material slurry is applied to the surface of an aluminum foil (thickness: 20 μm) which is a positive electrode current collector, dried at 120 ° C. for 3 minutes, and then compression-molded with a roll press to form a positive electrode having a rectangular planar shape. An active material layer was prepared. A positive electrode active material layer is formed on the back surface in the same manner, and a positive electrode active material layer having a thickness (excluding foil) of 60 μm is formed on both sides of the positive electrode current collector (aluminum foil) to prepare a positive electrode. bottom. The capacity of the positive electrode active material used per unit mass was 180 mAh / g. The amount of one-sided coating of the positive electrode active material layer was 23.5 mg / cm ² (excluding foil). The density was 3.0 g / cm ³ (not including foil).

2. Preparation of Negative Electrode As the carbon material as the negative electrode active material, natural graphite (1) having a Young's modulus of 30 GPa and natural graphite (2) having a Young's modulus of 15 GPa were prepared. The Young's modulus value of the carbon material was measured by the measuring method specified in JIS R 7222-1997. The average particle size (D50) of these natural graphites was 20 μm, respectively.

On the other hand, as a Si-containing alloy which is a negative electrode active material, a _{Si—Ti alloy represented by Si 60} Ti ₄₀ (unit: mass%) was prepared. The Si-containing alloy was produced by the mechanical alloy method. Specifically, a zirconia crushed ball and a raw material powder of an alloy were put into a zirconia crushed pot using a planetary ball mill device P-6 manufactured by Frichchu, Germany, and alloyed at 600 rpm for 48 hours. Then, the pulverization treatment was carried out at 400 rpm for 1 hour. As the raw material powder of the alloy, metal powders of Si and Ti were used. Here, the alloying treatment is to alloy the raw material powder of the alloy at a high rotation speed (600 rpm) by applying high energy. On the other hand, in the pulverization treatment, a treatment for loosening secondary particles is carried out at a low rotation speed (400 rpm) (the treatment does not alloy). The secondary particle size D50 of the obtained Si-containing alloy was 3.0 μm, and the capacity per unit mass was 660 mAh / g.

Using any of the above carbon materials and the above Si-containing alloy as the negative electrode active material, the negative electrode (1) to the negative electrode (5) were produced by the following methods by changing the mixed mass ratio of these.

(Preparation of negative electrode (1))
As a constituent component of the negative electrode active material layer, natural graphite (1) having a Young's modulus of 30 GPa is 4.05% by mass, and the Si—Ti alloy prepared above is 76.95% by mass (mixture of natural graphite and Si—Ti alloy). The mass ratio was 5:95), 2% by mass of VGCF and 2% by mass of carbon black (manufactured by IMERYS, Super-P®) as a conductive auxiliary agent, and 15% by mass of graphite as a binder were prepared. Next, N-methyl-2-pyrrolidone (NMP), which is a solvent for adjusting the viscosity of these component slurrys, is added to an appropriate amount, and the mixture is stirred and mixed for 10 minutes using a stirring defoaming machine to sufficiently disperse the negative electrode activity. A material slurry was prepared. The solid content ratio of the slurry was adjusted to 40% by mass. The solid content ratio indicates the ratio of the total mass of the negative electrode active material, the conductive auxiliary agent, and the binder to the slurry mass as a percentage.

The negative electrode active material slurry prepared above is applied to one side of a copper foil (thickness 10 μm) to be a negative electrode current collector, fired at 300 ° C. for 12 hours, and then compression-molded with a roll press to prepare a negative electrode. bottom. The amount of one-sided coating of the negative electrode active material layer was 8.6 mg / cm ² (excluding foil). That is, the amount of one-sided coating of the negative electrode active material layer was adjusted so that the A / C ratio between the negative electrode active material layer and the opposite positive electrode was 1.20 when the battery was manufactured, which will be described later. The thickness of the negative electrode active material layer (excluding the copper foil) was 45 μm.

(Preparation of negative electrode (2))
The mixing ratios of the natural graphite (1) and the Si—Ti alloy are 8.1% by mass and 72.9% by mass, respectively, so that the mixed mass ratio of the natural graphite (1) and the Si—Ti alloy is 10:90. The negative electrode (2) was produced by the same method as that for producing the negative electrode (1) described above. The amount of one-sided coating of the negative electrode active material was adjusted so that the A / C ratio was 1.20.

(Preparation of negative electrode (3))
The mixing ratios of the natural graphite (1) and the Si—Ti alloy are 12.15% by mass and 68.85% by mass, respectively, so that the mixed mass ratio of the natural graphite (1) and the Si—Ti alloy is 15:85. The negative electrode (3) was produced by the same method as that for producing the negative electrode (1) described above. The amount of one-sided coating of the negative electrode active material was adjusted so that the A / C ratio was 1.20.

(Preparation of negative electrode (4))
Except that only Si—Ti alloy was used as the negative electrode active material and natural graphite (1) was not used (the compounding ratios of natural graphite (1) and Si—Ti alloy were set to 0% by mass and 100% by mass, respectively). The negative electrode (4) was manufactured by the same method as that for the negative electrode (1) described above. The amount of one-sided coating of the negative electrode active material was adjusted so that the A / C ratio was 1.20.

(Preparation of negative electrode (5))
The mixing ratios of the natural graphite (1) and the Si—Ti alloy are 24.3% by mass and 56.7% by mass, respectively, so that the mixed mass ratio of the natural graphite (1) and the Si—Ti alloy is 30:70. The negative electrode (5) was produced by the same method as that for producing the negative electrode (1) described above. The amount of one-sided coating of the negative electrode active material was adjusted so that the A / C ratio was 1.20.

(Preparation of negative electrode (6))
The negative electrode (6) was produced by the same method as that of the negative electrode (1) described above, except that natural graphite (2) having a Young's modulus of 15 GPa was used instead of the natural graphite (1). The amount of one-sided coating of the negative electrode active material was adjusted so that the A / C ratio was 1.20.

3. 3. Preparation of Battery [Example 1]
The positive electrode prepared above and the negative electrode (1) prepared above were cut out so as to have an active material layer area of 4 cm in length and 3 cm in width, respectively, and a porous polypropylene separator (thickness 25 μm, porosity 55%) was formed. A power generation element was produced by laminating through (1 positive electrode and 2 negative electrodes). A positive electrode lead and a negative electrode lead were joined to each current collector of the obtained power generation element, and these positive electrode leads or negative electrode leads were joined to the positive electrode current collector plate and the negative electrode current collector plate, respectively. Then, the power generation element is inserted into an aluminum laminated sheet bag (length 4.5 cm x width 3.5 cm), which is a battery exterior material, so that the positive electrode current collector and the negative electrode current collector are exposed to the outside of the battery, and the liquid is injected. The electrolytic solution was injected through the opening by the machine. In this aluminum laminated sheet bag, two aluminum laminated sheets (a film sheet obtained by laminating aluminum with a film containing polypropylene) are laminated, and three of the four outer circumferences (outer edges) are thermocompression bonded. It is sealed (sealed) and the remaining one side is unsealed (opening). As the electrolytic solution, 1.0 M LiPF ₆ was dissolved in a 3: 7 (EC: DEC volume ratio) mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) with respect to 100 parts by mass of the solution. A mixture in which 1 part by mass of vinylene carbonate, which is an additive, was added was used. Here, the injection amount of the electrolytic solution was set to be 1.50 times the total pore volume (calculated by calculation) of the positive electrode active material layer, the negative electrode active material layer, and the separator. Next, under vacuum conditions, the opening of the aluminum laminated sheet bag is sealed by thermocompression bonding so that the positive electrode current collector and the negative electrode current collector connected to both electrodes (current collectors) via leads are led out. Then, the test cell (1), which is a laminated lithium ion secondary battery, was completed. When the rated capacity of the test cell (1) thus obtained was measured by the following method, it was 80 mAh (0.080 Ah).

(Measuring method of rated capacity)
The rated capacity of the battery (test cell) was determined by the following method. The test cell was held under normal temperature and pressure (25 ° C., atmospheric pressure) for 12 hours after injection (during this holding period, the opening of the laminated sheet bag after injection was heated under normal temperature and pressure. It was sealed by crimping, and the obtained test cell was set in the evaluation cell mounting jig). Then, at 25 ° C., the battery was charged to 4.2 V at a rate of 0.1 C by the constant current charging method, then paused for 10 minutes, charged for 2 hours by the constant voltage charging method, and then held for 24 hours. Then, it was discharged to 3V at 0.1C by the constant current discharge method, paused for 10 minutes, and then discharged at 3V for 2 hours by the constant voltage discharge method. The charge / discharge operation was repeated twice, and the sum of the second constant current discharge capacity and the constant voltage discharge capacity was defined as the rated capacity.

[Example 2]
A test cell (2), which is a laminated lithium ion secondary battery, was produced by the same method as in Example 1 described above except that the negative electrode (2) was used instead of the negative electrode (1). When the rated capacity of the test cell (2) thus obtained was measured by the same method as above, it was 82 mAh.

[Example 3]
A test cell (3), which is a laminated lithium ion secondary battery, was produced by the same method as in Example 1 described above except that the negative electrode (3) was used instead of the negative electrode (1). When the rated capacity of the test cell (3) thus obtained was measured by the same method as above, it was 83 mAh.

[Comparative Example 1]
A test cell (4), which is a laminated lithium ion secondary battery, was produced by the same method as in Example 1 described above except that the negative electrode (4) was used instead of the negative electrode (1). When the rated capacity of the test cell (4) thus obtained was measured by the same method as above, it was 78 mAh.

[Comparative Example 2]
A test cell (5), which is a laminated lithium ion secondary battery, was produced by the same method as in Example 1 described above except that the negative electrode (5) was used instead of the negative electrode (1). When the rated capacity of the test cell (5) thus obtained was measured by the same method as above, it was 83 mAh.

[Comparative Example 3]
A test cell (6), which is a laminated lithium ion secondary battery, was produced by the same method as in Example 1 described above except that the negative electrode (6) was used instead of the negative electrode (1). When the rated capacity of the test cell (6) thus obtained was measured by the same method as above, it was 79 mAh.

4. Evaluation of Battery Characteristics For each battery (test cell) produced above, charging / discharging at a 0.5 C rate was repeated for 100 cycles at 25 ° C. When evaluating the battery, the charging condition was a constant current constant voltage charging method in which the battery was charged at a rate of 0.5 C until the maximum voltage reached 4.2 V, and then held for about 1 hour to 1.5 hours. The discharge condition was a constant current discharge method in which the battery was discharged at a rate of 0.5 C until the minimum voltage of the battery became 3.0 V. All were performed under normal temperature and pressure (25 ° C., atmospheric pressure). Then, the ratio of the discharge capacity in the 100th cycle to the discharge capacity in the first cycle was evaluated as a "capacity retention rate (%)". The results obtained are shown in Table 1 below.

Further, the initial volume energy density (Ah / L) was measured as a value obtained by dividing the discharge capacity in the first cycle by the volume of the test cell. The volume of the test cell was calculated by measuring the length, width, and thickness of the cell. The obtained results are shown in Table 1 below as relative values when the volumetric energy density of the test cell (4) of Comparative Example 1 is set to 100%.

As can be seen from the results shown in Table 1, a carbon material having a relatively large Young's modulus of 30 GPa is used in combination with a Si-containing alloy as a negative electrode active material, and the content ratio of the carbon material in the total content of these is 5 to 5. By controlling to the range of 15% by mass, it is possible to achieve excellent cycle durability (capacity retention rate) while sufficiently securing the initial discharge capacity (energy density).

10,50 Lithium-ion secondary battery,
11 Negative electrode current collector,
12 Positive electrode current collector,
13 Negative electrode active material layer,
15 Positive electrode active material layer,
17 Electrolyte layer (separator),
19 Single battery layer,
21,57 Power generation elements,
25 Negative current collector plate,
27 Positive electrode current collector plate,
29, 52 Battery exterior material,
58 Positive tab,
59 Negative electrode tab.

Claims (3)

With the current collector
A negative electrode active material layer containing a negative electrode active material arranged on the surface of the current collector, and a negative electrode active material layer.
Negative electrode for non-aqueous electrolyte secondary batteries
The negative electrode active material is selected from the group consisting of a Si-containing alloy, graphite, non-graphitized carbon, and amorphous carbon, and has a Young's modulus of 30 GPa or more measured by the measuring method specified in JIS R 7222-1997. Including carbon material,
A negative electrode for a non-aqueous electrolyte secondary battery, wherein the content ratio of the carbon material to the total content of the Si-containing alloy and the carbon material is 5 to 15% by mass. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material layer contains polyimide as a binder. A non-aqueous electrolyte secondary battery using the negative electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2.

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