JP6862752B2 - Negative electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery using this - Google Patents

Description

The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same. The negative electrode for a non-aqueous electrolyte secondary battery according to the present invention and the non-aqueous electrolyte secondary battery using the same include, for example, an electric vehicle (EV), a fuel cell vehicle (FCV), an ethanol FCV, and a plug-in, which are next-generation eco-cars. It is used as a driving power source and an auxiliary power source for motors and the like of vehicles such as FCVs, plug-in hybrid vehicles (PHVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

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 EVs, FCVs, ethanol FCVs, plug-in FCVs, PHVs, HEVs and PHEVs. .. Lithium-ion secondary batteries intended for application to electric vehicles are required to have a large capacity and a large area.

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 electric vehicles (HEVs), electric vehicles (EVs), and fuel cell vehicles. .. Lithium-ion secondary batteries intended for application to electric vehicles are required to have a large capacity (high capacity) and a large area.

Conventionally, a carbon material such as graphite, which is advantageous in terms of charge / discharge cycle life and cost, has been used as a negative electrode active material 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 the above 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 that of the graphite material, whereas that of the Si material is about 4 times that of the Si material, which shifts from the amorphous state to the crystalline state when Si and Li are alloyed. 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 a negative electrode active material using a Si material, there is a trade-off relationship between capacity and cycle durability, and there is a problem that it is difficult to improve cycle durability while exhibiting high capacity.

To solve these problems, for example, the formula: comprising amorphous Si alloy having a Si _x M _y Al _z, negative electrode active material has been proposed for a lithium ion secondary battery. Here, x, y, z in the formula represent atomic percentage values, and x + y + z = 100, x ≧ 55, y <22, z> 0, M are Mn, Mo, Nb, W, Ta, Fe, Cu, It is a metal composed of at least one of Ti, V, Cr, Ni, Co, Zr, and Y. It is described that the negative electrode active material for a lithium ion secondary battery containing such an amorphous Si alloy exhibits a good cycle life in addition to a high capacity by minimizing the content of the metal M. Further, it is described that a good cycle life is exhibited by mixing a graphite material having a small expansion.

However, it has been found that sufficient charge / discharge cycle characteristics cannot be achieved even by the technique using the Si-containing alloy (Si alloy) described above, and further by the technique of mixing the Si alloy and the graphite material. That is, in the technique described above, due to a large volume change of the Si alloy material, the negative electrode active material layer containing the Si alloy also causes a large volume change, causing peeling at the interface between the active material layer and the current collector, and electrically. There was a problem of losing the network and reducing the cycle durability.

In order to solve this problem, for example, by arranging a graphite layer with a small volume change near the current collector and arranging a mixture layer containing Si on it, peeling at the interface between the active material layer and the current collector can be achieved. A method of suppressing has been proposed (see, for example, Patent Document 1).

JP-A-2002-358954 Special Table 2009-517850

According to the studies by the present inventors, it has been found that sufficient charge / discharge cycle characteristics are still not achieved by the technique described in Patent Document 2. In this method, peeling at the interface between the active material layer and the current collector can be suppressed, but since the volume change of the graphite layer and the mixture layer containing Si is significantly different, the mixture layer containing the graphite layer and Si It was found that peeling occurred at the interface, which reduced the cycle durability.

Therefore, an object of the present invention is to provide a means (particularly, a negative electrode for a non-aqueous electrolyte secondary battery) capable of achieving sufficient charge / discharge cycle characteristics while maintaining a high capacity in a non-aqueous electrolyte secondary battery. To do.

The present inventors control the mixing ratio of the carbon material and the Si material in the negative electrode for a non-aqueous electrolyte secondary battery containing the Si material and the carbon material as the active material, and the amount of the Si material from the current collector side to the positive electrode facing side. It was found that the above-mentioned problems can be solved by using an active material layer in which the amount of carbon dioxide is gradually increased. Based on such findings, the present invention has been completed.

The present invention contains a Si material and a carbon material as active materials, and when the content of the Si material of the active material layer is α and the content of the carbon material is β (mass%), the mixing ratio of the carbon material and the Si material is 80 ≦ α + β. The negative electrode is controlled so as to satisfy ≦ 98, 0.1 ≦ α ≦ 40, and 58 ≦ β ≦ 97.9. In addition to the above requirements, when the active material layer cross section is evenly divided into three in the thickness direction, the area of the Si material in each divided area increases by 1% or more and 12% or less from the current collector side to the positive electrode facing surface side. To provide a negative electrode.

In the present invention, by using an inclined electrode in which the mixing ratio of the Si material increases by an appropriate amount from the current collector side to the positive electrode facing surface side, there are few Si materials having a large volume change in the vicinity of the current collector. Damage and peeling of the active material layer are reduced. As a result, by maintaining the electron conductivity in the charge / discharge process, it is possible to maintain a high capacity, significantly improve the discharge capacity retention rate, and achieve both capacity and cycle durability.

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. FIG. 3A shows a negative electrode active material slurry in which the solid content ratio is adjusted in order to produce a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material increases by an appropriate amount from the current collector side to the positive electrode facing surface side. It is sectional drawing which represented typically the state of application to an electric body. FIG. 3B shows the coated surface formed in FIG. 3A below the coated surface formed in FIG. 3A in order to manufacture a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material increases by an appropriate amount from the current collector side to the positive electrode facing surface side. It is a cross-sectional view schematically showing the state (turned over) toward. FIG. 3 (c) shows the coated surface facing downward in FIG. 3 (b) in order to manufacture a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material increases by an appropriate amount from the current collector side to the positive electrode facing surface side. It is sectional drawing which shows typically the state which adjusted the drying temperature in the state (turned over) and dried at low temperature, and formed the negative electrode. FIG. 3D schematically represents a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material increases by an appropriate amount from the current collector side to the positive electrode facing surface side, which is an embodiment of the negative electrode according to the present invention. It is a sectional view. FIG. 4A is a drawing showing a reflected electron image (measurement image) taken by an electron microscope (SEM) of the negative electrode of Comparative Example 1-1. FIG. 4B is a process obtained by grayscale the measurement image of FIG. 4A by a binarization process and setting a threshold value between the grayscale value of the Si material portion and the portion other than the Si material portion. It is a drawing which shows an image (the white part in a figure corresponds to a Si material part). Further, in FIG. 4B, the cross section of the negative electrode active material layer is evenly divided into three in the electrode thickness direction for the processed image, and the cross section (divided section) divided into three is seen from the positive electrode facing surface (surface; separator) side. The symbols A, B, and C are attached in order toward the current collector side.

Hereinafter, embodiments of the present invention 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.

According to one embodiment of the present invention, it is 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 layer has the following formula (1).

(In the formula, the Si material is a material made of an alloy containing Si, and α and β represent the mass% of each component in the negative electrode active material layer, 80 ≦ α + β ≦ 98, 0.1 ≦ α ≦ 40, 58 ≦ β ≦ 97.9), and when an arbitrary place in the negative electrode surface is selected, the negative electrode active material layer cross section is evenly divided into three in the electrode thickness direction. At that time, the area of the Si material in each divided area is increased by 1% or more and 12% or less from the current collector side to the positive electrode facing surface (surface) side. A negative electrode for a secondary battery is provided. Further, according to one embodiment of the present invention, a positive electrode having (a) the negative electrode, (b) a current collector, and a positive electrode active material layer containing a positive electrode active material arranged on the surface of the current collector. , (C) A non-aqueous electrolyte secondary battery comprising a power generation element including a separator is provided. In the present embodiment, by having such a configuration, the effects of the above invention can be effectively exhibited.

The details of why the above-mentioned effect can be obtained by the negative electrode for a non-aqueous electrolyte secondary battery of the present invention and the non-aqueous electrolyte secondary battery using the same are unknown, but the following mechanism of action (mechanism of action) Can be considered. The following mechanism of action is speculative, and the present invention is not limited to the following mechanism of action.

In the negative electrode of the present embodiment, a high capacity can be maintained and sufficient charge / discharge cycle characteristics can be exhibited by using an inclined electrode in which the mixing ratio of the Si material increases by an appropriate amount from the current collector to the side facing the positive electrode. As a result, both capacity and cycle durability can be achieved at the same time. Although the mechanism of action is not clear, the inclined electrode of this embodiment is compared with an electrode (existing normal electrode) having no inclination (the mixing ratio of Si material does not increase or decrease from the current collector to the opposite side of the positive electrode). Therefore, the structure (structure) is such that there are few Si alloy materials having a large volume change in the vicinity of the current collector. Therefore, damage to the current collector and peeling of the active material layer are reduced, and electron conductivity is maintained during the charging / discharging process, so that the discharge capacity retention rate can be significantly improved while maintaining high capacity. Be done. On the other hand, in the inclined electrode (reverse inclined electrode) in which the mixing ratio of the Si alloy decreases from the current collector to the side opposite to the positive electrode, the structure (structure) is such that there are many Si alloy materials having a large volume change in the vicinity of the current collector. .. Therefore, it is considered that the active material layer is peeled off and the current collector is deformed in the vicinity of the current collector, the active material is largely dropped off, and the cycle durability is lowered. Further, in the inclined electrode (excessively inclined electrode) in which the mixing ratio of the Si material exceeds 12% from the current collector to the side facing the positive electrode, the rate of increase in the mixing ratio of the Si material is too high (structure). Therefore, since the volume change rate in each block divided into three in the electrode thickness direction is too large, peeling occurs between the blocks (particularly, near the boundary between regions where the increase rates are significantly different), and the cycle durability is lowered. it is conceivable that.

Hereinafter, the basic configuration of the non-aqueous electrolyte secondary battery using the negative electrode for the non-aqueous electrolyte secondary battery according to the present invention will be described. In this embodiment, a lithium ion secondary battery will be described as an example.

First, in the lithium ion secondary battery of the present embodiment, the voltage of the cell (single battery layer) is large, and high energy density and high output density can be achieved. Therefore, the lithium ion secondary battery of the present embodiment is excellent as a drive power source for a vehicle or an auxiliary power source. As a result, it can be suitably used as a lithium ion secondary battery for driving a vehicle. In addition to this, it is fully applicable to lithium ion secondary batteries for mobile devices such as mobile phones.

When the lithium ion secondary battery is distinguished by its form and structure, it can be applied to any conventionally known form and structure such as a laminated type (flat type) battery and a wound type (cylindrical type) battery. It is a thing. By adopting a laminated (flat type) battery structure, long-term reliability can be ensured by simple thermocompression bonding and other sealing technologies, which is advantageous in terms of cost and workability.

In addition, 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 type (internal parallel connection type) batteries and bipolar type (internal series connection type) batteries. It is a thing.

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 non-aqueous electrolyte secondary battery according to the present invention and the lithium ion secondary battery according to the present embodiment should not be limited to these.

<Overall structure of battery>
FIG. 1 shows the overall structure of a flat type (laminated type) lithium ion secondary battery (hereinafter, also simply referred to as “laminated type battery”), which is a typical embodiment of the non-aqueous electrolyte secondary battery of the present invention. Is a schematic cross-sectional view schematically showing.

As shown in FIG. 1, the laminated battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminated sheet 29 which is an exterior body. .. Here, the power generation element 21 has a positive electrode in which positive electrode active material layers 15 are arranged on both sides of the positive electrode current collector 12, an electrolyte layer (separator) 17, and negative electrode active material layers 13 on both sides of the negative electrode current collector 11. It has a structure in which the formed negative electrode is laminated. Specifically, one positive electrode active material layer 15 and a negative electrode active material layer 13 adjacent thereto are opposed to each other via an electrolyte layer 17, and a negative electrode, an electrolyte layer, and a positive electrode are laminated in this order. ..

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 the negative electrode current collectors of the outermost layers located on 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 positive electrode current collector of the outermost layer is located on both outermost layers of the power generation element 21, and one side of the positive electrode current collector of the outermost layer or The positive electrode active material layer may be arranged on both sides.

The positive electrode current collector 12 and the negative electrode current collector 11 are attached with a positive electrode current collector plate 27 and a negative electrode current collector plate 25 that are electrically connected to each electrode (positive electrode and negative electrode), and are sandwiched between the ends of the laminate sheet 29. It has a structure that is led out to the outside of the laminated sheet 29. 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. In the present embodiment, the positive electrode active material is not particularly limited, but preferably contains a lithium nickel-based composite oxide or a spinel-based lithium manganese composite oxide, and more preferably contains a lithium nickel-based composite oxide. The ratio of the total amount of the lithium nickel-based composite oxide and the spinel-based lithium manganese composite oxide to 100% by mass of the total amount of the positive electrode active material contained in the positive electrode active material layer is preferably 50% by mass or more, and more. It is preferably 70% by mass or more, more preferably 85% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

(Lithium-nickel-based composite oxide)
The composition of the lithium-nickel-based composite oxide is not specifically limited as long as it is a composite oxide containing lithium and nickel. A typical example of a composite oxide containing lithium and nickel is a lithium nickel composite oxide (LiNiO ₂ ). However, a composite oxide in which a part of the nickel atom of the lithium nickel composite oxide is replaced with another metal atom is more preferable, and as a preferable example, a lithium-nickel-manganese-cobalt composite oxide (hereinafter, simply "NMC composite"). (Also referred to as "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, and is one of the transition metal M. It contains one Li atom per atom, and the amount of Li that can be taken out is twice that of spinel-based lithium manganese oxide, that is, the supply capacity is doubled, and it can have a high capacity. In addition, since it _{has higher thermal stability than LiNiO 2} , it is particularly advantageous among nickel-based composite oxides used as positive electrode active materials.

As used herein, NMC composite oxides also include composite oxides in which some of the transition metal elements are replaced by other metal elements. 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, preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, and more preferably Ti, Zr, P, Al, Mg, It is Cr, and more preferably Ti, Zr, Al, Mg, and Cr from the viewpoint of improving cycle characteristics.

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, b + c + d = 1. It has a composition represented by (at least one of the elements selected from Ti, Zr, 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. From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the general formula (1). 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, it is preferable that a part of the transition element is substituted with another metal element, and it is particularly 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.

As a more preferable embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31 and 0.19 ≦ d ≦ 0.26. Is preferable in that the balance between capacity and durability is excellent.

Lithium-nickel-based composite oxides such as NMC composite oxides can be prepared by selecting various known methods such as a coprecipitation method and a spray-drying method. Since the composite oxide according to this embodiment can be easily prepared, it is preferable to use the coprecipitation method. Specifically, as a method for synthesizing the NMC composite oxide, for example, as in the method described in JP-A-2011-105588, a nickel-cobalt-manganese composite oxide is produced by a coprecipitation method, and then nickel-cobalt-manganese composite oxide is produced. It can be obtained by mixing a cobalt-manganese composite oxide and a lithium compound and firing them. Hereinafter, a specific description will be given.

The raw material compound of the composite oxide, for example, the Ni compound, the Mn compound and the Co compound, is dissolved in a suitable solvent such as water so as to have the composition of the desired active material. Examples of Ni compounds, Mn compounds and Co compounds include sulfates, nitrates, carbonates, acetates, oxalates, oxides, hydroxides and halides of the metal element. Specific examples of the Ni compound, Mn compound and Co compound include, but are not limited to, nickel sulfate, cobalt sulfate, manganese sulfate, nickel acetate, cobalt acetate, manganese acetate and the like. In this process, if necessary, as a metal element that replaces a part of the layered lithium metal composite oxide constituting the active material so as to obtain a desired composition of the active material, for example, Ti, Zr, Nb. , W, P, Al, Mg, V, Ca, Sr and Cr and other compounds containing at least one metal element may be further mixed.

A coprecipitation reaction can be carried out by a neutralization / precipitation reaction using the above raw material compound and an alkaline solution. As a result, a metal composite hydroxide and a metal composite carbonate containing the metal contained in the raw material compound can be obtained. As the alkaline solution, for example, an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia or the like can be used, but it is preferable to use sodium hydroxide, sodium carbonate or a mixed solution thereof for the neutralization reaction. .. In addition, it is preferable to use an aqueous ammonia solution or an ammonium salt for the complex reaction.

The amount of the alkaline solution used in the neutralization reaction may be an equivalent ratio of 1.0 with respect to the neutralized content of all the metal salts contained therein, but it is preferable to add the excess alkaline content together for pH adjustment.

The amount of the aqueous ammonia solution or ammonium salt added for the complex reaction is preferably such that the concentration of ammonia in the reaction solution is in the range of 0.01 to 2.00 mol / l. The pH of the reaction solution is preferably controlled in the range of 10.0 to 13.0. The reaction temperature is preferably 30 ° C. or higher, more preferably 30 to 60 ° C.

The composite hydroxide obtained by the coprecipitation reaction is then preferably suction filtered, washed with water, and dried. By adjusting the conditions (stirring time, alkali concentration, etc.) when performing the co-precipitation reaction, the particle size of the composite hydroxide can be controlled, and this is the secondary of the positive electrode active material that is finally obtained. It affects the average particle size (D50) of the particles.

Next, a lithium-nickel-manganese-cobalt composite oxide can be obtained by mixing the nickel-cobalt-manganese composite hydroxide with a lithium compound and firing the mixture. Examples of the Li compound include lithium hydroxide or a hydrate thereof, lithium peroxide, lithium nitrate, lithium carbonate and the like.

The firing treatment may be performed in one step, but is preferably performed in two steps (temporary firing and main firing). A composite oxide can be efficiently obtained by firing in two steps. The tentative firing conditions are not particularly limited, and it is difficult to unambiguously define them because they differ depending on the lithium raw material. Here, as factors for controlling the average primary particle size and crystallite size, the firing temperature and firing time at the time of firing (temporary firing and main firing in the case of two stages) are particularly important. It is possible to control the average primary particle size and crystallite size by adjusting based on the following tendencies. That is, as the firing time is lengthened, the average primary particle size and crystallite size increase. Further, as the firing temperature is increased, the average primary particle diameter and the crystallite diameter increase. The rate of temperature rise is preferably 1 to 20 ° C./min from room temperature. Further, the atmosphere is preferably in the air or in an oxygen atmosphere. Here, in the case of synthesizing the NMC composite oxide using lithium carbonate as the Li raw material, the calcination temperature is preferably 500 to 900 ° C., more preferably 600 to 800 ° C., and further preferably 650. ~ 750 ° C. Further, the calcination time is preferably 0.5 to 10 hours, more preferably 4 to 6 hours. On the other hand, the conditions for the main firing are not particularly limited, but the heating rate is preferably 1 to 20 ° C./min from room temperature. Further, the atmosphere is preferably in the air or in an oxygen atmosphere. Further, in the case of synthesizing an NMC composite oxide using lithium carbonate as a Li raw material, the calcination temperature is preferably 800 to 1200 ° C., more preferably 850 to 1100 ° C., and further preferably 900 to 1050 ° C. ℃. Further, the calcination time is preferably 1 to 20 hours, more preferably 8 to 12 hours.

If necessary, when a small amount of a metal element that replaces a part of the layered lithium metal composite oxide constituting the active material is added, the method includes a method of mixing with nickel, cobalt, and manganate in advance. Any means may be used, such as a method of adding nickel, cobalt, and manganate at the same time, a method of adding to the reaction solution during the reaction, and a method of adding to the nickel-cobalt-manganese composite oxide together with the Li compound.

The lithium nickel-based composite oxide can be produced by appropriately adjusting the reaction conditions such as the pH of the reaction solution, the reaction temperature, the reaction concentration, the addition rate, and the stirring time.

(Spinel-based lithium manganese composite oxide)
The spinel-based lithium manganese composite oxide is a composite oxide which has _{a composition of LiMn 2} O ₄ and has a spinel structure and which essentially contains lithium and manganese, and its specific composition and production method. As for, conventionally known findings such as JP-A-2000-77071 can be appropriately referred to.

Needless to say, a positive electrode active material other than the above-mentioned lithium nickel-based composite oxide or spinel-based lithium manganese composite oxide may be used. When two or more types of positive electrode active materials are used in combination, if the optimum particle size for exhibiting the unique effect of each active material is different, the optimum particle size for exhibiting each unique effect is selected. It may be used by blending, and it is not always necessary to make the particle size of all active materials uniform.

The average particle size of the positive electrode active material contained in the positive electrode active material layer 15 is not particularly limited, but from the viewpoint of increasing the output, the secondary particle size is preferably 6 to 11 μm, more preferably 7 to 10 μm. The average particle size of the primary particles is 0.4 to 0.65 μm, more preferably 0.45 to 0.55 μm. The "particle size" in the present specification means the maximum distance L among the distances between arbitrary two points on the contour line of the particles. Further, as the value of the "average particle size", an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) is used, and the average particle size of the particles observed in several to several tens of fields is averaged. The value calculated as the value shall be adopted. As the secondary particle size (average particle size D50), a value obtained by a laser diffraction method may be used.

Further, the positive electrode active material layer preferably contains a binder and a conductive auxiliary agent in addition to the above-mentioned positive electrode active material. Further, if necessary, it further contains an electrolyte (polymer matrix, ionic conductive polymer, electrolytic solution, etc.) and other additives such as a lithium salt for enhancing ionic conductivity.

The content of the positive electrode active material capable of functioning as the active material in the positive electrode active material layer is preferably 85 to 99.5% by mass.

(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. Examples of the conductive auxiliary agent include carbon black such as acetylene black, ketjen black and furnace black, carbon powder such as channel black, thermal black and graphite, and various carbon fibers such as vapor-grown carbon fiber (VGCF; registered trademark). , Carbon materials such as expanded graphite. 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 electrolyte salt (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 the lithium ion secondary battery.

The positive electrode (positive electrode active material layer) is coated with a normal slurry, or 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. Can be formed.

[Negative electrode active material layer]
The negative electrode active material layer 13 has the following formula (1).

(In the formula, the Si material is a material made of an alloy containing Si (Si alloy), and α and β represent mass% of each component of the negative electrode active material in the negative electrode active material layer, and 80 ≦ α + β ≦ 98, One of the features is that it contains a negative electrode active material represented by (0.1 ≦ α ≦ 40, 58 ≦ β ≦ 97.9).

That is, the negative electrode active material layer 13 indispensably contains a Si alloy and a carbon material, which are Si materials, as the negative electrode active material. Hereinafter, these negative electrode active materials will be described in detail.

(Si alloy)
The alloy containing Si, which is one of the negative electrode active materials (Si 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 _{alloy, Si x Ti y Ge za,} 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 < Binary alloys such as x <100, 0 <y <100, 0 ≦ z <100, and 0 ≦ a <0.5, x + y + z + a = 100) or 3 Amorphous alloys and the like can be mentioned. By using these Si alloys as the negative electrode active material, the predetermined first additive element (binary alloy) and the predetermined second additive element (ternary alloy) can be appropriately selected to form a Li alloy. At the same time, it is possible to suppress the phase transition of the amorphous-crystal and improve the cycle life. Further, as a result, the capacity becomes higher than that of the conventional negative electrode active material, for example, a carbon-based negative electrode active material.

(Average particle size of Si alloy (secondary particle size) D50)
The average particle size of the Si alloy may be about the same as the average particle size of the negative electrode active material contained in the existing negative electrode active material layer 13, and is not particularly limited. From the viewpoint of durability and high output, the average particle size (secondary particle size) D50 of the Si alloy is preferably in the range of 1 to 20 μm, more preferably 1 to 15 μm, and further preferably 1 to 10 μm. .. Further, preferably, the average particle size (secondary particle size) D90 of the Si alloy 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 alloy. 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 alloy is not particularly limited and may be spherical, elliptical, columnar, polygonal, scaly, amorphous or the like. In the present embodiment, for the D50 value, the D50; median diameter, that is, the particle size of the intermediate value is calculated based on the particle size distribution data calculated by the laser particle size distribution meter, and the value is adopted. Further, in the present embodiment, the laser particle size distribution meter is a laser diffraction / scattering type particle size distribution measuring device (manufactured by HORIBA, Ltd., model: LA-920) or the like, which uses the same measurement principle. A scattering type particle size distribution measuring device can be used. The measuring method can be widely applied to other particles such as positive electrode active material particles, negative electrode active material particles (Si alloy powder, carbon material powder), conductive auxiliary agent and the like.

(Supporting (coating) of carbon-based material on the surface of Si alloy)
In the present embodiment, it is preferable that the Si alloy is carbon-coated. A negative electrode active material containing a Si alloy in which the Si alloy is carbon-coated and a carbon-based material is supported (coated) on the surface (hereinafter, also simply referred to as “carbon-supported Si alloy” or “carbon-coated Si alloy”) was used. Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are excellent in that they have high cycle durability. The carbon-based material used here is a carbon material that does not correspond to an active material because it cannot be repeatedly charged and discharged (conductive), that is, an active material having low crystallinity in which Li ion insertion / desorption does not easily occur or does not occur. It is preferable to use a carbon material that does not meet the definition of (conductive).

As used herein, "supporting" or "coating" means that the carbon-based material is chemically or physically bonded to the surface of at least a part of the Si alloy. Whether or not the carbon-based material is supported (coated) on the surface of the Si alloy is observed in the carbon-supported Si alloy manufactured or collected (separated) from the electrode in a state where the carbon-based material is attached to the Si alloy particles. It can be confirmed by. In the present embodiment, the case where the coverage of the Si alloy particles with the carbon-based material is 15 mol% or more is considered to be a state in which the carbon-based material is supported (coated) on the surface of the Si alloy. For this reason, the negative electrode active material, the conductive auxiliary agent (carbon-based material; this conductive auxiliary agent also usually uses a (conductive) carbon material that does not correspond to the active material) and the binder as conventionally used. Depending on the simple mixing, the conductive additive is not supported on the negative electrode active material, or the coverage of the Si alloy with the carbon-based material is less than 15 mol%. The state of the carbon-based material supported (coated) on the surface of the Si alloy can be easily confirmed by a known means such as a scanning electron microscope (SEM).

The detailed reason why the cycle durability of a lithium ion secondary battery or the like using a carbon-supported Si alloy obtained by carbon-coating the above-mentioned Si alloy is improved is unknown, but the following reasons are as follows. Conceivable.

As described above, the Si alloy, which is a Si material, has more expansion and contraction during charging and discharging than the carbon material (graphite, etc.), which is an active material. Deterioration of cycle durability has been a problem due to (oxidation) and the like. Further, the formulas described above "Background _Art": The Si _x M y lithium ion secondary battery using the anode having an amorphous alloy having Al _{z, wherein:} a amorphous alloy having a Si _x M y Al _z However, as with the high-purity Si active material, expansion and contraction cannot be sufficiently suppressed. Therefore, the specific surface area of the active material increases due to the miniaturization of the active material (particles) due to expansion and contraction during charging and discharging, the decomposition of the electrolytic solution is promoted, and the side reaction is generated by the depletion of the electrolytic solution and the decomposition of the electrolytic solution. Objects are formed and interfere with conductivity.

Further, since the above-mentioned amorphous alloy contains Si (semiconductor), sufficient conductivity cannot be ensured. Therefore, when the amorphous alloy is used as an active material, it is necessary to add a conductive auxiliary agent, but it is difficult to disperse uniformly with the addition of a conventional conductive auxiliary agent, and the conductivity is locally high. In many cases, the structure was a mixture of active material and low active material. For these reasons, it has been difficult to maintain high cycle characteristics with conventional techniques.

On the other hand, in the present embodiment, a carbon-rich carbon material and a Si alloy, which is a Si material, are used in combination as the negative electrode active material, and the carbon-based material is further supported (coated) on the surface of the Si alloy. The action and effect of this embodiment can be exhibited more remarkably. That is, the presence of the carbon-based material on the surface of the Si alloy can further suppress the reactivity between the surface of the Si alloy (particles) and the electrolytic solution. Therefore, it is possible to further suppress the excessive decomposition reaction of the electrolytic solution and the accompanying formation of side reactants. Further, unlike the conventional method of simply adding a conductive auxiliary agent, the carbon-based material having high conductivity exists on the surface of the Si alloy (particles), so that the conductivity of the Si alloy (particles) is ensured and Si. High conductivity can be imparted to the entire alloy. As a result, for example, when applied to a lithium ion secondary battery, when Li ions are inserted, the effect of further promoting uniform charging depth of Si alloy particles is brought about, and excessive Li ions are inserted and deteriorated. It is possible to further eliminate Si alloy particles that are easily facilitated.

That is, when a carbon material and the above-mentioned carbon-supported Si alloy are used as the negative electrode active material, the carbon-based material, not the Si alloy particles, comes into contact with the electrolytic solution, so that the decomposition reaction of the electrolytic solution (particularly by silicon) is further suppressed. It can be suppressed, and the conductivity can be further improved by the presence of the carbon-based material on the outermost surface. Therefore, when a carbon material and the above-mentioned carbon-supported Si alloy are used as the negative electrode active material, it is excellent in that the cycle characteristics, as well as the initial capacity and the cycle characteristics can be further improved.

The mechanism of action is speculative, and the present embodiment is not limited to the mechanism of action.

As described above, in this embodiment, it is desirable that the carbon-based material is supported (coated) on the surface of the Si alloy (particles). Here, the coverage (supporting ratio) of the Si alloy with the carbon-based material is not particularly limited as long as it is 15 mol% or more as described above. Considering the effect of further improving the cycle characteristics (cycle durability), the effect of further improving the conductivity, and the like, the coverage of the Si alloy with the carbon-based material is preferably 50 to 400 mol%, more preferably. Is 100 to 400 mol%, and even more preferably 250 to 400 mol%.

In the present specification, the value measured and calculated by the following method is adopted as the “coating ratio (supporting ratio) of the Si alloy with the carbon-based material”. In addition, in this specification, "covering ratio (supporting ratio) (mol%) by carbon-based material of Si alloy" is also simply referred to as "carbon covering ratio (mol%)".

<Measurement of coverage (supporting rate) of Si alloy with carbon-based material>
The carbon coverage of the Si alloy on which the carbon-based material is supported is measured under the following measurement conditions by using Auger electron spectroscopy to measure the molar ratio of silicon and the molar ratio of carbon.

Next, using the molar ratio of silicon and the molar ratio of carbon measured above, the molar ratio of carbon to the molar ratio of silicon was calculated according to the following formula, and the obtained value was calculated as the carbon coverage (mol%). And.

Here, the method of controlling the coverage (supporting ratio) of the Si alloy with the carbon-based material within the above-mentioned preferable range is not particularly limited. Specifically, the Si alloy and the carbon-based material are mixed in an appropriate ratio and then physically or chemically treated to chemically or physically bond (support) the carbon-based material to the Si alloy surface. You can use the method of making it.

In the above method, the mixing ratio of the Si alloy and the carbon-based material is not particularly limited. Specifically, when the total amount of the Si alloy and the carbon-based material is 100 parts by weight, the ratio of the carbon-based material is preferably 1 to 25 parts by weight, more preferably 5 to 25 parts by weight. In particular, it is mixed with the Si alloy in a proportion of 10 to 25 parts by weight. According to such a mixing ratio, the coverage (supporting ratio) of the carbon-based material of the Si alloy can be easily controlled within the above-mentioned preferable range. Further, according to such a mixing ratio, the carbon-based material can be uniformly supported (coated) on the surface of the Si alloy.

The carbon-based material is not particularly limited, and a carbon-based material usually used as a conductive auxiliary agent can be used. Specifically, acetylene black, furnace black, carbon black, channel black, and graphite (which are pulverized to the same extent as conductive aids and are clearly different from carbon materials, which are active materials, from the viewpoint of particle size. It is something that can be distinguished). Of these, from the viewpoint of support retention, the carbon-based material cannot be repeatedly charged and discharged as described above, so that the conductive carbon material that does not correspond to the active material, that is, the insertion and desorption of Li ions is unlikely or does not occur. It is preferably a conductive carbon material having low crystallinity. Specifically, it is preferable to use acetylene black and carbon fiber. Further, the shape of the carbon-based material is also not particularly limited, and may be in the form of particles or fibers. The particle form is preferable from the viewpoint of ease of carrying, and the fiber form is preferable from the viewpoint of conductivity. The size of the carbon-based material is also not particularly limited as long as it is pulverized to the same extent as the conductive auxiliary agent and is clearly distinguished from the carbon material which is the active material from the viewpoint of particle size. .. For example, when the carbon-based material is in the form of particles, the average particle size (secondary particle size) is preferably 10 to 200 nm, more preferably 20 to 150 nm. When the carbon-based material is in the form of fibers, the diameter is preferably 20 to 500 nm, more preferably 50 to 300 nm, and the length is preferably 5 to 20 μm, more preferably 8. It is ~ 15 μm. With such a size, the carbon-based material can be easily supported on the Si alloy surface. Further, with such a size, the carbon-based material can be uniformly supported on the Si alloy surface.

Further, in the above method, the physical or chemical treatment method for chemically or physically bonding (supporting) the carbon-based material to the Si alloy surface is not particularly limited. For example, a method of embedding at least a part of a carbon-based material in a Si alloy by shearing, a method of chemically bonding via a functional group on the surface of the Si alloy and the carbon-based material, and the like can be mentioned. More specifically, a mechanochemical method, a liquid phase method, a sintering method, a vapor phase deposition (CVD) method and the like can be mentioned.

The physical or chemical treatment conditions for chemically or physically bonding (supporting) the carbon-based material to the Si alloy surface are not particularly limited and can be appropriately selected depending on the method used. For example, when the mechanochemical method is used, the rotation speed (processing rotation speed) is preferably 3000 to 8000 rpm, more preferably 4000 to 7000 rpm. The load power is preferably 200 to 400 W, more preferably 250 to 300 W. The treatment time is preferably 10 to 60 minutes, more preferably 20 to 50 minutes. Under such conditions, the carbon-based material can be supported (coated) on the Si alloy surface with the above-mentioned preferable coating rate (supporting rate). Further, the carbon-based material can be uniformly supported on the surface of the Si alloy.

(Manufacturing method of Si alloy)
The method for producing the Si alloy according to this embodiment is not particularly limited, and can be produced by using various conventionally known productions. Examples of the manufacturing method of the Si 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 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 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 alloy can be realized. For example, a simple substance constituting a Si 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 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.

By performing the alloying treatment described above, a structure composed of a matrix phase / silicide phase can be obtained. In particular, if the alloying treatment time is 12 hours or more, a non-aqueous electrolyte secondary battery capable of exhibiting desired cycle durability can be obtained. The alloying treatment time is preferably 24 hours or more, more preferably 30 hours or more, further preferably 36 hours or more, still more preferably 42 hours or more, and particularly preferably 48 hours. That is all. The upper limit of the time for the alloying treatment is not particularly set, but it is usually 72 hours or less. Further, among the above-mentioned alloying treatments, in the case of the alloying treatment by the mechanical alloying method, a conventionally known method can be used. For example, by using a ball mill device (for example, a planetary ball mill device), the crushed balls and the raw material powder of the alloy are put into the crushing pot, the rotation speed is increased, and high energy is applied, so that alloying can be achieved. The rotation speed (rotational speed) of the ball mill device is, for example, 500 rpm or more, preferably 600 rpm or more.

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.

Further, 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 and the like onto a current collector. May be further pulverized. 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 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. 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.

(Carbon material)
The carbon material, which is one of the negative electrode active materials, is not particularly limited, but is graphite (graphite), which is a highly crystalline carbon such as natural graphite and artificial graphite; soft carbon (easy-graphitized carbon), hard carbon (non-graphitized). Low-crystalline carbon such as carbon); carbon black (atypical carbon) such as Ketjen black, acetylene black, channel black, lamp black, oil furnace black, thermal black; fullerene, carbon nanotubes, carbon nanofibers, carbon nanohorns, etc. Examples include carbon materials such as carbon fibrils. Of these, it is preferable to use graphite (graphite), which is a highly crystalline carbon such as natural graphite or artificial graphite. These carbon materials may be used alone or in combination of two or more. In order for the carbon material to be used as an active material for a secondary battery, any carbon material that is prone to insertion and desorption of Li ions (can be repeatedly charged and discharged) may be used.

In the present embodiment, by using a carbon material as the negative electrode active material together with the above Si alloy so as to be carbon-rich, high capacity can be maintained, higher charge / discharge cycle characteristics can be exhibited, and capacity and cycle durability can be exhibited. Can be achieved at the same time.

The shape of the carbon material is not particularly limited and may be spherical, elliptical, columnar, polygonal, scaly, amorphous or the like.

(Average particle size of carbon material (secondary particle size) D50)
The average particle size of the carbon material is not particularly limited, but the average particle size (secondary particle size) D50 is preferably 5 to 50 μm, more preferably 5 to 25 μm, and 12 to 25 μm. It is more preferable to have. Here, the value obtained by the laser diffraction method is used as the average particle size (secondary particle size) of the carbon material. In the present embodiment, for the D50 value, the D50; median diameter, that is, the particle size of the intermediate value is calculated based on the particle size distribution data calculated by the laser particle size distribution meter, and the value is adopted. Further, in the present embodiment, the laser particle size distribution meter is a laser diffraction / scattering type particle size distribution measuring device (manufactured by HORIBA, Ltd., model: LA-920) or the like, which uses the same measurement principle. A scattering type particle size distribution measuring device can be used. At this time, with respect to the comparison with the average particle size of the above-mentioned Si alloy, the average particle size of the carbon material may be the same as or different from the average particle size of the Si alloy, but it is preferable that the average particle size is different. .. In particular, it is more preferable that the average particle size of the Si alloy, which is a Si material, is smaller than the average particle size of the carbon material. Further, the ratio (A / C) of the average particle size (secondary particle size) D50 (A) of the Si alloy, which is a Si material, to the average particle size (secondary particle size) D50 (C) of the carbon material is 0. It is preferably less than 5, more preferably 0.3 or less, and even more preferably 0.1 or less. When the average particle size (secondary particle size) D50 (C) of the carbon material is relatively larger than the average particle size (secondary particle size) D50 (A) of the Si alloy which is the Si material, the carbon material is uniformly The particles are arranged, and the Si alloy particles are arranged in the gaps between the particles of the carbon material. Further, in this embodiment, when the cross section of the negative electrode active material layer is evenly divided into three in the electrode (negative electrode active material layer) thickness direction, the area of the Si alloy, which is the Si material, within each divided area is on the current collector side. It has a configuration in which it is arranged so as to increase by 1% or more and 12% or less from the surface to the positive electrode facing surface (surface) side. That is, it has a configuration in which more Si alloys are arranged in the gaps between the particles of the carbon material on the positive electrode facing surface (surface) side than on the current collector side. In such a configuration, for example, as shown in Examples, the solid content concentration of the negative electrode active material (aqueous) slurry is adjusted to a predetermined (narrow) range, and the subsequent drying temperature is also adjusted to a predetermined (narrow) range. Can be achieved with (see Examples). In addition to the above, if the particle size of the Si alloy, which is a Si material with a relatively large capacity, is equivalent to the particle size of a carbon material with a small capacity, even if it can be dispersed evenly, the negative electrode active material The volume distribution in the layer plane (direction) tends to vary slightly. Therefore, by reducing the particle size of the Si alloy, which is a Si material having a relatively large capacity, it is possible to further reduce the variation in capacity in the plane (direction) of the negative electrode active material layer. The lower limit of the ratio (A / C) of the average particle size (secondary particle size) D50 (A) of the Si alloy to the average particle size (secondary particle size) D50 (C) of the carbon material is not particularly limited. , For example, 0.01 or more. From the above, by making the particle size of the Si alloy, which is a Si material having a relatively large capacity, smaller than the particle size of the carbon material, a more uniform charge / discharge reaction can be promoted, and the performance (capacity and durability) can be promoted. (Sex) can be further improved. Further, the variation in capacity in the negative electrode active material layer plane can be further reduced, and the performance (capacity and durability) can be further improved.

As described above, the Si alloy, which is a Si material, has a slight variation in the surface (direction) of the negative electrode active material layer (all Si alloy particles are evenly arranged in the gaps between the particles of all the carbon materials in the negative electrode active material layer surface). It may not be evenly arranged due to some variations that may occur if it is not done. In such a case, the potentials and capacities developed by _{the respective SiO x and Si alloys are different.} As a result, in the SiO _x and Si alloy of the anode active material layer includes a SiO _x and Si alloy that reacts with excessive lithium ion, SiO _x and Si alloy that does not react with lithium ions occur. That is, non-uniformity of the reaction of _{SiO x} and Si alloy with lithium ions in the negative electrode active material layer occurs. Then, the negative electrode active of SiO _x and Si alloy material layer, by SiO _x and Si alloy acts excessively react excessively lithium ion, significant decomposition reaction and excess electrolyte by the electrolyte _{The structure of the SiO x} and Si alloys can be destroyed by the expansion. As a result, excellent even when using SiO _x and Si alloys has a characteristic, uniform in the case of such SiO _x and Si alloy is not disposed, the cycle characteristics as the non-aqueous electrolyte secondary battery Can decrease.

However, _{mixing the SiO x} and Si alloy with a carbon material can solve the above problem. More specifically, _{by mixing the SiO x} and Si alloys with the carbon material, the SiO _x and Si alloys can be arranged in a well-balanced manner (relatively uniformly dispersed (dispersed)) in the negative electrode active material layer. Can be. _{As a result, it is considered that both SiO x} and Si alloys in the negative electrode active material layer show the same reactivity and can prevent deterioration of the cycle characteristics. _{This is because SiO x} particles and Si alloy particles can enter the gaps between the particles of the carbon material having a high content _{, so that the SiO x} and Si alloys are well-balanced (relatively uniformly dispersed (dispersed)). It is thought that it can be placed. As a result, the contact area between each particle is increased, electrical conductivity can be ensured, _{and both SiO x} and Si alloys can exhibit the same reactivity (prevent non-uniformity of reaction), so that the cycle It is considered that deterioration of characteristics can be prevented. That is, however, in the present embodiment, the concentration gradient is positively provided in the Si alloy in the negative electrode active material layer thickness direction so as to exert the effect of the above invention, but as described above, the negative electrode active material layer in-plane (direction). ), It can be said that it is preferable that there is no variation.

As a result of mixing the carbon materials so as to be carbon-rich, the content of the Si alloy in the negative electrode active material layer is relatively reduced, so that the initial capacity can be reduced. However, since the carbon material itself is an active material and has reactivity with lithium ions (the insertion and desorption of Li ions are likely to occur), the degree of decrease in the initial capacity is relatively small. That is, the negative electrode active material according to the present embodiment has a large effect of improving the cycle characteristics as compared with the action of lowering the initial capacity.

Further, the carbon material is less likely to undergo a volume change when reacting with lithium ions when compared with the Si alloy which is a Si material. Therefore, even when the volume change of the Si alloy, which is a Si material, is large, as a result of mixing the carbon materials so as to be carbon-rich, the negative electrode active material as a whole is the negative electrode active material associated with the lithium reaction. The effect of volume change can be relatively minor. It should be noted that such an effect can be understood from the results of the examples in which the higher the carbon material content (the smaller the Si material content), the higher the cycle characteristics.

Further, by containing a carbon material, the electric energy consumption (Wh) can be improved. More specifically, the carbon material has a relatively low potential as compared with the Si material (Si alloy). As a result, the relatively high potential of the Si material can be reduced. Then, since the potential of the entire negative electrode is lowered, the power consumption (Wh) can be improved. Such an action is particularly advantageous when used in, for example, vehicle applications.

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 as long as it does not affect (do not impair) the action and effect of the present embodiment. 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, and a lithium alloy-based negative electrode material. Of course, other negative electrode active materials may be used.

The negative electrode active material layer contains a negative electrode active material represented by the following formula (1).

In the formula (1), the Si material and the carbon material in parentheses represent essential components of the negative electrode active material. Here, the Si material is a material made of an alloy containing Si (Si alloy). Further, α and β represent the contents (mass%) of the Si material and the carbon material in the negative electrode active material layer, and are 80 ≦ α + β ≦ 98, 0.1 ≦ α ≦ 40, and 58 ≦ β ≦ 97.9. is there.

As is clear from the formula (1), the content (α) of the Si material in the negative electrode active material layer is 0.1 to 40% by mass. The content (β) of the carbon material is 58 to 97.9% by mass. Further, the total content (α + β) of these is 80 to 98% by mass.

The mixing ratio of the Si material and the carbon material of the negative electrode active material is not particularly limited as long as the above content specification is satisfied, and can be appropriately selected depending on the desired application and the like. In this embodiment, the content of the Si material is relatively low and the content of the carbon material is relatively high as the mixing ratio of the Si material and the carbon material (furthermore, a specific concentration of the Si material in the thickness direction). By forming a gradient), the action and effect of this embodiment can be effectively exhibited. Among them, the content of the Si material (α) in the negative electrode active material is preferably in the range of 0.5 to 40% by mass, more preferably 1 to 30% by mass, and further preferably 1 to 20% by mass. .. If the content of the Si material in the negative electrode active material layer is less than 0.1% by mass, it is difficult to obtain a high initial capacity. On the other hand, if the content of the Si material exceeds 40% by mass, high cycle characteristics cannot be obtained. The content of the carbon material (β) in the negative electrode active material is preferably in the range of 58 to 97.5% by mass, more preferably 68 to 97% by mass, and further preferably 78 to 97% by mass. If the content of the carbon material in the negative electrode active material layer is less than 58% by mass, high cycle characteristics cannot be obtained. On the other hand, if the content of the carbon material exceeds 97.9% by mass, it is difficult to obtain a high initial capacity.

The total content (α + β) of the Si material and the carbon material in the negative electrode active material layer is not particularly limited as long as the above-mentioned content (α and β) of each component is satisfied, and is appropriately selected according to a desired application and the like. it can. Among them, the total content (α + β) of the Si material and the carbon material in the negative electrode active material layer is preferably in the range of 80 to 98% by mass, more preferably 85 to 97% by mass, and further preferably 90 to 97% by mass. is there. If the total content (α + β) of the Si material and the carbon material in the negative electrode active material layer is less than 80% by mass, the weight energy density becomes low, which is not preferable. On the other hand, if the total content (α + β) of the Si material and the carbon material in the negative electrode active material layer exceeds 98% by mass, the binder and the conductive auxiliary agent are insufficient, which causes deterioration of the battery performance, which is not preferable.

(Binder)
In this embodiment, the negative electrode active material layer preferably contains a binder. The binder contained in the negative electrode active material layer preferably 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.

Specific examples of the aqueous binder include styrene-based polymers (styrene-butadiene rubber (SBR), styrene-vinyl acetate copolymer, styrene-acrylic copolymer, etc.), acrylonitrile-butadiene rubber, and methyl methacrylate-butadiene rubber. , (Meta) acrylic polymers (polyethyl acrylate, polyethyl methacrylate, polypropyl acrylate, polymethyl methacrylate (methyl rubber methacrylate), polypropyl methacrylate, polyisopropyl acrylate, polyisopropyl methacrylate, polybutyl acrylate, polybutyl methacrylate, Polyhexyl acrylate, polyhexyl methacrylate, polyethylhexyl acrylate, polyethylhexyl methacrylate, polylauryl acrylate, polylauryl methacrylate, etc.), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polybutadiene, butyl rubber, fluororubber, poly Examples thereof include ethylene oxide, polyepicchlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, polyester resin, phenol resin and epoxy resin. These water-based binders may be used alone or in combination of two or more.

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 an aqueous binder is used, it is preferable to use a thickener in combination. This is because the water-based binder has a strong binding property (binding effect), but the viscosity is not sufficiently increased. Therefore, a sufficient thickening effect cannot be obtained simply by adding an aqueous binder to the aqueous slurry at the time of producing the electrode. Therefore, by using a thickener having an excellent viscosity thickening agent, the water-based binder is imparted with a thickening agent. The thickener is not particularly limited, and for example, polyvinyl alcohol (the average degree of polymerization is preferably 200 to 4000, more preferably 1000 to 3000, and the degree of saponification is preferably 80 mol%. As described above, more preferably 90 mol% or more) and 1 to 80 mol% of the vinyl acetate unit of the polymer having a molar ratio of ethylene / vinyl acetate = (2/98) to (30/70). Kensate, 1 to 50 mol% partial acetal compound of polyvinyl alcohol, etc.), starch and its modified products (oxidized starch, phosphoric acid esterified starch, cationized starch, etc.), cellulose derivatives (carboxymethyl cellulose (CMC), methyl cellulose, hydroxy, etc.) Copolymers of propyl cellulose, hydroxyethyl cellulose, and salts thereof), polyvinylpyrrolidone, polyacrylic acid (salt), polyethylene glycol, (meth) acrylamide and / or (meth) acrylate [(meth) acrylamide polymer , (Meta) acrylamide- (meth) acrylate copolymer, alkyl (meth) acrylate (1 to 4 carbon atoms) ester- (meth) acrylate copolymer, etc.], styrene-maleate copolymer Combined, Mannig modified polyacrylamide, formalin condensed resin (urea-formalin resin, melamine-formalin resin, etc.), polyamide polyamine or dialkylamine-epicchlorohydrin copolymer, polyethyleneimine, casein, soybean protein, synthetic protein, and galacto Examples include a mannan derivative and the like. These thickeners may be used alone or in combination of two or more.

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 variants, starch and its variants, 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.

When the negative electrode active material layer contains a binder, the content of the aqueous binder among the binders used in the negative electrode active material layer is preferably 80 to 100% by mass, preferably 90 to 100% by mass, and 100. It is preferably mass%. Examples of the binder other than the water-based binder include a binder (organic solvent-based binder) used for the positive electrode active material layer.

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 2 to 4% by mass, and most preferably 2.5 to 3% by mass. 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. The amount of the thickener contained in the negative electrode active material layer is the mass ratio of the aqueous binder (SBR) and the thickener, the amount of the binder contained in the negative electrode active material layer, and the negative electrode active material layer. It is obtained from the content of the water-based binder in the contained binder.

(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. Although not particularly limited, carbon black such as acetylene black, ketjen black and furnace black, carbon powder such as channel black, thermal black and graphite, and various carbon fibers such as vapor-grown carbon fiber (VGCF; registered trademark), Examples include carbon materials such as expanded graphite. 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.

When the conductive auxiliary agent is a carbon powder, its average particle size is not particularly limited, but from the viewpoint of improving conductivity, the secondary particle size is preferably 100 to 500 nm, more preferably 100 to 300 nm. The average particle size of the primary particles is 10 to 100 nm, more preferably 20 to 80 nm. When the conductive auxiliary agent is carbon fiber, the average fiber diameter thereof is not particularly limited, but is preferably 10 to 80 nm, more preferably 10 to 50 nm from the viewpoint of improving strength and conductivity. From the viewpoint of forming an electronic network, the average fiber length of the carbon fibers is 5 to 20 μm, more preferably 10 to 15 μm. The "fiber diameter" in the present specification means the maximum distance L among the distances between arbitrary two points on the contour line of the cross section perpendicular to the longitudinal direction of the carbon fiber. Further, the value of the "average fiber diameter" is set in the longitudinal direction of the carbon fiber observed in several to several tens of fields by using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). A value calculated as an average value of fiber diameters in a vertical cross section shall be adopted. As used herein, the term "fiber length" means the length (distance) of carbon fibers in the longitudinal direction. Further, as the value of the "average fiber length", an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) is used, and the value is in the longitudinal direction of the carbon fiber observed in several to several tens of fields. The value calculated as the average value of the length (fiber length) shall be adopted. As the conductive auxiliary agent on the positive electrode side, the same size (average particle size) as the conductive auxiliary agent on the negative electrode side can be used.

The content of the conductive auxiliary agent in the negative 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.

(Lithium salt)
The lithium salt is contained in the negative electrode active material layer when the above-mentioned electrolyte permeates into the negative electrode active material layer. Therefore, the specific form of the lithium salt that can be contained in the negative electrode active material layer is the same as that of the lithium salt that constitutes the electrolyte. 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.

(Ion conductive polymer)
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 negative electrode active material layer is not particularly limited. The compounding ratio can be adjusted by appropriately referring to known knowledge about the lithium ion secondary battery.

The negative electrode (negative 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 thickness of each 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 each active material layer is usually about 1 to 500 μm, preferably about 2 to 100 μm, in consideration of the purpose of use of the battery (emphasis on output, emphasis on energy, etc.) and ionic conductivity.

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

(Structure of negative electrode active material layer of inclined electrode structure)
In this embodiment, when an arbitrary location is selected in the surface of the negative electrode active material layer, when the cross section of the negative electrode active material layer is evenly divided into three in the electrode thickness direction, the area of the Si material in each divided area collects electricity. It is characterized in that it increases by 1% or more and 12% or less from the body side to the side facing the positive electrode. With such a configuration (inclined electrode structure in which the mixing ratio of the Si material increases by an appropriate amount from the current collector to the side facing the positive electrode), since there are few Si materials having a large volume change in the vicinity of the current collector, the current collector can be used. Damage and peeling of the active material layer are reduced. As a result, by maintaining the electron conductivity in the charge / discharge process, it is possible to maintain a high capacity, significantly improve the discharge capacity retention rate, and achieve both capacity and cycle durability.

When an arbitrary location is selected in the surface of the negative electrode active material layer, when the cross section of the negative electrode active material layer is evenly divided into three in the electrode thickness direction, the area of the Si material in each divided area is on the current collector side. From 1% to 10% or less, more preferably 3% or more and 10% or less, further preferably 5% or more and 10% or less, and particularly preferably 6% or more and 10% or less. It is good to do it. By setting the inclined electrode structure (the rate of increase in the area of the Si material in each of the divided areas) within the above-mentioned preferable range, the cycle durability (discharge capacity retention rate, etc.) of the battery is further improved. be able to.

FIG. 3A shows a negative electrode active material slurry in which the solid content ratio is adjusted in order to produce a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material increases by an appropriate amount from the current collector side to the positive electrode facing surface side. It is sectional drawing which represented typically the state of application to an electric body. FIG. 3B shows the coated surface formed in FIG. 3A below the coated surface formed in FIG. 3A in order to manufacture a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material increases by an appropriate amount from the current collector side to the positive electrode facing surface side. It is a cross-sectional view schematically showing the state (turned over) toward. FIG. 3 (c) shows the coated surface facing downward in FIG. 3 (b) in order to manufacture a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material increases by an appropriate amount from the current collector side to the positive electrode facing surface side. It is sectional drawing which shows typically the state which adjusted the drying temperature in the state (turned over) and dried at low temperature, and formed the negative electrode. It can be said that FIG. 3D is a cross-sectional view schematically showing a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material increases by an appropriate amount from the current collector side to the positive electrode facing surface side.

As a method of increasing the area of the Si material in each of the divided areas by the above range, mainly, the solid content ratio in the negative electrode active material slurry is adjusted, the slurry is applied to the current collector, and then the coated surface is coated. Drying downward and adjusting the drying temperature (low temperature drying) may be performed. Specifically, when preparing the negative electrode active material slurry, the solid content ratio in the slurry (active material weight + conductive auxiliary agent weight + thickener weight + total solid content weight such as binder powder weight / slurry weight) Is 35 to 45% by weight. By doing so, it becomes easy to reduce the viscosity of the slurry and give it a slope. As shown in FIG. 3 (a), this slurry is coated (coated) on the current collector (current collector foil) 31 to form a coating film (coating film) 31, and then FIG. 3 (b). As shown in FIG. 3C, the coating film (coating film) is dried in a low temperature environment of 40 to 90 ° C. with the 31 side facing down. By doing so, the Si material (Si alloy) 35 is closer to the positive electrode facing surface side due to the relationship between the specific gravity of the Si material (Si alloy) active material particles 35 and the carbon material active material particles 37, and the negative electrode activity having an inclined electrode structure is provided. The material layer 33 (negative electrode 30) can be produced. That is, as shown in FIG. 3D, in the negative electrode 30 of the present embodiment, the negative electrode active material layer 33 on the current collector 31 is formed by the above method to form the Si material active material particles 35 and the carbon material active material. Due to the specific gravity of the particles 37, the Si material active material particles 35 have an inclined electrode structure closer to the positive electrode facing surface side. In order to make the slurry more inclined, it is preferable that the solid content ratio in the slurry is 36 to 43% by mass and the drying temperature is in the range of 40 to 70 ° C. In addition to the above method, the drying time may be further changed for adjustment. Specifically, it may be dried at the above drying temperature for 6 to 18 hours, preferably 12 to 18 hours. Alternatively, three or more types having different solid content ratios in the negative electrode active material slurry may be prepared, coated and dried in this order to form a negative electrode active material layer having a laminated structure of three or more layers, which is particularly limited. It's not something. In the mass production process, a roll-to-roll method is used, and a die coater is used for a strip-shaped (ribbon-shaped) current collector that is drawn out from a roll-shaped current collector and conveyed to a slurry on the back surface of the current collector. May be applied (coated) and dried while being transported as it is. Alternatively, a strip-shaped (ribbon-shaped) current collector that is drawn out from a roll-shaped current collector and transported is coated (coated) with a slurry on the surface of the current collector using a die coater, and then the slurry is applied. The current collector may be dried while being conveyed in a twisted (inverted) state at 180 ° C.

As an arbitrary place in the surface of the negative electrode active material layer, the negative electrode active material is used from the viewpoint of measuring the inclined electrode structure (the area ratio of the Si material in each of the divided areas) in the electrode thickness direction of the negative electrode active material layer. It may be anywhere in the layer plane and is not particularly limited. For example, an arbitrary location may be appropriately selected, such as near the end portion in the surface of the negative electrode active material layer, near the central portion, or near the intermediate portion between the end portion and the central portion.

(Method of calculating the ratio of the area of Si material in each of the above divided areas)
The method for calculating the area ratio (%) of the Si material (Si alloy) within each of the divided areas in the negative electrode active material layer is not limited, but for example, the negative electrode active material layer cross section shown below. There is a method by image processing. That is, after the negative electrode is cross-sectioned by an arbitrary cross-section processing method so as to include an arbitrary measurement point in the surface of the negative electrode active material layer, the negative electrode cross section of the measurement point is subjected to a secondary electron image or reflection with an electron microscope. An electron image is imaged (see FIG. 4 (a)). Image processing software is used for the image (reflected electron image). The image processing software is not limited, and for example, Carl Zeiss's AxioVision, Mitani Corporation's WinROOF, Media Cybernetics' Image-Pro, and the like can be used. In the binarization process (image processing) using image processing software, after the measurement image (reflected electron image) is grayscaled, it is appropriate between the grayscale value of the Si material part and the part other than the Si material part. A processed image is obtained by setting a different threshold value. For the obtained processed image, the cross section of the negative electrode active material layer is evenly divided into three in the electrode thickness direction, and for each of the three divided cross sections (divided section), Si in the area of the divided processed image (negative electrode active material layer cross section). Obtain the amount of area of the material part. Then, the area ratio of the Si material portion to the total area of the divided processed image (the area of the Si material / the area of the entire divided measurement image × 100 (%)) is calculated. As a method of setting an appropriate threshold value, in addition to setting the value itself of either the Si material or the material other than the Si material part (carbon material, etc.) as the threshold value, a method of setting an intermediate value between the two values as the threshold value. Some methods can be applied depending on the degree of difference between the two grayscale values. A method of setting an intermediate value between the two numerical values as a threshold value is preferable.

Specifically, the secondary electron image or backscattered electron image (see FIG. 4A) imaged with an electron microscope is binarized and grayscaled with respect to the negative electrode cross section of the measurement location, and the threshold value is set. To obtain a processed image (see FIG. 4B). With respect to this processed image, the cross section of the negative electrode active material layer that does not include the current collector on one side is evenly divided into three in the thickness direction (see FIG. 4B). Then, the ratio (%) of the area of the Si material (Si alloy) in each divided area is calculated (using the above image processing software). For example, when the thickness of the negative electrode active material layer (one side) is 60 μm, the processed image (see FIG. 4B) is divided into 20 μm increments in the thickness direction, and within each divided (image) area. Calculate the area ratio (%) of the Si material (Si alloy).

The visual field area of the secondary electron image or backscattered electron image imaged with an electron microscope with respect to the negative electrode cross section of the measurement point is not particularly limited, but for example, the negative electrode active material layer whose vertical direction (thickness direction) is on one side. It may be one that includes all the thicknesses (see FIG. 4A), and the width (direction perpendicular to the thickness direction) may be in the range of about 50 to 200 μm. In the embodiment, as shown in FIG. 4A, the visual field area of the reflected electron image of the negative electrode cross section is 70 μm in the vertical direction (thickness direction) including the entire thickness of the negative electrode active material layer on one side, and is horizontal (thickness). The image was taken so that the field of view perpendicular to the vertical direction) was a rectangular field of view of 100 μm.

Any location (measurement location) in the negative electrode active material layer surface may be selected from one location or a plurality of locations (two or more locations), but the inclined electrode structure in the electrode thickness direction in the negative electrode active material layer plane may be selected. Since there is almost no variation depending on the measurement location in the negative electrode active material layer surface, it can be said that one location (for example, near the central portion in the negative electrode active material layer surface) may be measured. That is, the cross section of the negative electrode active material layer may be calculated from one image data. Also in the examples, one location near the central portion in the negative electrode active material layer plane was selected (calculated from one image data). When the electrode area is large as in the case of a large battery described later, it is preferably 2 in consideration of some non-uniformity of the electrode structure in the manufacturing process (acceptable fluctuation error of the composition in the active material layer plane). It is preferable to take the average value of 5 or more images (2 locations), more preferably 5 images (5 locations) or more. However, in addition to the large battery, the average value of two or more image data (two places) may be taken in the same manner.

<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.

When a thin film alloy is directly formed on the negative electrode current collector 11 by a sputtering method or the like for the negative electrode active material, it is preferable to use a current collector foil.

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 contains at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene.

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 microporous (microporous membrane) separators made of (structured laminates, etc.), hydrocarbon resins such as polyethylene, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), and glass fibers.

The thickness of the microporous (microporous membrane) separator cannot be uniquely specified because it differs depending on the intended use. For example, in applications such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and secondary batteries for driving motors such as fuel cell vehicles (FCVs), the length is 4 to 60 μm in a single layer or multiple layers. 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 as a supporting 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 compounds 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-vinylethylenecarbonate, 1-ethyl-2-vinylethylenecarbonate, vinylvinylene carbonate, allylethylenecarbonate, vinyl Oxymethylethylene carbonate, allyloxymethylethylene carbonate, acrylicoxymethylethylene carbonate, methacryloxymethylethylene carbonate, ethynylethylene carbonate, propargylethylene carbonate, ethynyloxymethylethylene carbonate, propargyloxyethylene carbonate, methyleneethylene carbonate, 1,1- Examples thereof include dimethyl-2-methyleneethylene carbonate. Of these, vinylene carbonate, methylvinylene carbonate and vinylethylene carbonate are preferable, and vinylene carbonate and vinylethylene carbonate are more preferable. Only one of these cyclic carbonates may be used alone, or two or more thereof 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 polymers 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 polymer electrolyte (for example, PEO or PPO) is subjected to thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. It may be polymerized.

(Separator with heat-resistant insulating layer)
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 or the inorganic particles and the porous substrate (resin porous substrate layer). The binder stably forms the heat-resistant insulating layer and prevents peeling between the porous substrate (porous substrate layer) 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 (porous substrate layer) 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 to the outside of a laminate film which is an exterior material for the purpose of taking out a 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).

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. Further, in the winding type lithium ion battery, the terminal may be formed by using, for example, a cylindrical can (metal can) instead of the tab.

<Seal part>
The seal portion is a member peculiar to the series laminated battery and has a function of preventing leakage of the electrolyte layer. In addition to this, it is also possible to prevent adjacent current collectors from coming into contact with each other in the battery and short circuits due to slight irregularities at the ends of the laminated electrodes.

The constituent material of the seal portion is not particularly limited, but polyolefin resins such as polyethylene and polypropylene, epoxy resins, rubber, polyimide and the like can be used. Of these, a polyolefin resin is preferably used from the viewpoints of corrosion resistance, chemical resistance, film forming property, economy, and the like.

<Positive terminal lead and negative electrode terminal lead>
As the material of the negative electrode and positive electrode terminal leads, the reeds used in known laminated secondary batteries can be used. The part taken out from the battery exterior material is heat-resistant and insulating so that it does not come into contact with peripheral devices or wiring and leak electricity, affecting 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 bags; see Examples) are more preferred. 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. To.

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. 1 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.

The lithium ion secondary battery is not limited to a laminated flat battery. The wound lithium-ion secondary battery may have a cylindrical shape, or may be formed by deforming such a cylindrical shape into a rectangular flat shape. There are no particular restrictions. The cylindrical shape is not particularly limited, for example, a laminated film may be used for the exterior material, or a conventional cylindrical can (metal can) may be used. Preferably, the power generation element is exteriorized with an aluminum laminate film. By this form, weight reduction can be achieved.

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. Further, in the winding type lithium ion battery, the terminal may be formed by using, for example, a cylindrical can (metal can) instead of the tab.

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

Therefore, in the present embodiment, 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.

[Volume energy density and rated (discharge) capacity]
Considering the mileage (cruising range) of one charge of the electric vehicle, the volumetric energy density of the battery is preferably 157 Wh / L or more, and the rated capacity is preferably 20 Ah or more.

Here, from the viewpoint of a large-sized battery, which is different from the viewpoint of the physical size of the electrode, the size of the battery is defined from the relationship between the battery volume and the battery capacity (rated capacity). Specifically, in the non-aqueous electrolyte secondary battery according to this embodiment, the value of the ratio of the battery volume (the product of the projected area and the thickness of the battery including the battery exterior) to the rated capacity is 10 cm ³ / Ah or less. It is preferable that the battery has a rated capacity of 3 Ah or more. This large-sized battery has a large battery capacity per unit volume (10 Ah / cm ³ or more), in other words, a small battery volume per unit capacity (ratio of the battery volume to the rated capacity) (10 cm ³ / Ah or less). Moreover, it is specified that the battery capacity (rated capacity) is large (3 Ah or more). It can be said that this can be applied to a large battery having a large capacity and a larger expansion than before by using a Si material and a carbon material in combination with the negative electrode active material.

The upper limit of the ratio of the battery volume (the product of the projected area and the thickness of the battery including the battery exterior) to the rated capacity is preferably 8 cm ³ / Ah or less. On the other hand, the lower limit of the value of the ratio of the battery volume (the product of the projected area and the thickness of the battery including the battery exterior) to the rated capacity is not particularly limited, but is preferably 2 cm ³ / Ah or more. More preferably, it is 3 cm ³ / Ah or more. The rated capacity is preferably 5 Ah or more, more preferably 10 Ah or more, still more preferably 15 Ah or more, particularly preferably 20 Ah or more, and particularly preferably 25 Ah or more. It is said that it is possible to achieve both vehicle required performance (high capacity and excellent cycle durability) and mounting space for the first time by using a large area (large volume) and large capacity battery with the battery volume and rated capacity within the above range. There are advantages. On the other hand, even a battery having a large area (large volume) and not a large capacity as described above, such as a conventional consumer battery, can satisfy the vehicle required performance (high capacity and excellent cycle durability).

The rated capacity of the battery is determined by the following.

≪Measurement of rated capacity≫
The rated capacity of the test battery is such that after injecting the electrolytic solution, the test battery is left to stand for about 10 hours, and then the temperature is 25 ° C. (within ± 2.5 ° C.; atmospheric temperature), 3.0 V to 4.15 V. In the voltage range, it is measured by steps 1-5 below.

Step 1: After reaching 4.15V with a constant current charge of 0.1C, rest for 5 minutes.

Step 2: After step 1, charge with constant voltage charging for 1.5 hours and rest for 5 minutes.

Step 3: After reaching 3.0 V by constant current discharge of 0.1 C, discharge by constant voltage discharge for 2 hours, and then rest for 10 seconds.

Step 4: After reaching 4.1 V by constant current charging of 0.1 C, charge by constant voltage charging for 2.5 hours, and then rest for 10 seconds.

Step 5: After reaching 3.0 V by constant current discharge of 0.1 C, discharge by constant voltage discharge for 2 hours, and then stop for 10 seconds.

Rated capacity: The rated capacity is the discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in step 5.

The battery volume is obtained by multiplying the projected area and the thickness of the battery including the battery exterior. Of these, regarding the projected area of the battery including the battery exterior, the projected area of the six batteries, front, back, right side, left side, flat surface, and bottom surface, can be obtained, and the largest projected area of the battery is obtained. Is usually used, and is usually the projected area of the battery on a flat surface or a bottom surface when the battery is placed on a flat plate in the most stable state. In addition, the thickness of the battery including the battery exterior shall be measured when fully charged. Further, since the thickness of the battery including the battery outer body is a large area, eight or more points are measured in consideration of the variation depending on the measurement points, and these are averaged values. For example, the thickness of the battery including the battery exterior can be measured at or near the points represented by the numbers 1 to 9 shown in FIG. 2, and the average value of these can be used. However, the measurement location is not limited to the example of FIG.

Further, the aspect ratio of the rectangular electrode is preferably 1 to 4, and 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 within such a range, there is an advantage that both vehicle required performance and mounting space can be achieved.

<Manufacturing method of lithium ion secondary battery>
The method for producing the lithium ion secondary battery is not particularly limited, and the lithium ion secondary battery can be produced by a known method. Specifically, it includes (1) fabrication of electrodes, (2) fabrication of a cell cell layer, (3) fabrication of a power generation element, and (4) fabrication of a laminated battery. Hereinafter, a method for manufacturing a lithium ion secondary battery will be described with an example, but the present invention is not limited thereto. In the above (1) fabrication of the electrode, in the fabrication of the inclined electrode in which the mixing ratio of the Si material (Si alloy) increases by an appropriate amount from the current collector to the side facing the positive electrode as in the negative electrode of the present embodiment, the following is performed. It can be produced by the means (conditions) described.

(1) Preparation of Electrodes (Positive Electrode and Negative Electrode) For the electrodes (positive electrode or negative electrode), for example, an active material slurry (positive electrode active material slurry or negative electrode active material slurry) is prepared, and the active material slurry is applied onto the current collector. It can be made by drying, then pressing. The active material slurry contains the above-mentioned active material (positive electrode active material or negative electrode active material), a binder (when an aqueous binder is used on the negative electrode side, it is desirable to use a thickener in combination), a conductive auxiliary agent and a solvent. In order to control the variation in the dispersibility of the binder (and the additive such as the conductive additive) in the surface of the electrode active material layer, it is mainly used when stirring using ultrasonic vibration during the production of the electrode active material slurry. The vibration time, ultrasonic wavelength, and the like may be changed for adjustment. In addition to this, the dispersion (stirring and mixing) time at the time of producing the electrode active material slurry may be mainly changed for adjustment. Specifically, it may be dried at the above drying temperature for 6 to 18 hours, preferably 12 to 18 hours. Alternatively, three or more types having different solid content ratios in the negative electrode active material slurry may be prepared, coated and dried in this order to form a negative electrode active material layer having a laminated structure of three or more layers, which is particularly limited. It's not something. In the mass production process, a roll-to-roll method is used, and a die coater is used for a strip-shaped (ribbon-shaped) current collector that is drawn out from a roll-shaped current collector and conveyed to a slurry on the back surface of the current collector. May be applied (coated) and dried while being transported as it is. Alternatively, a strip-shaped (ribbon-shaped) current collector that is drawn out from a roll-shaped current collector and transported is coated (coated) with a slurry on the surface of the current collector using a die coater, and then the slurry is applied. The current collector may be dried while being conveyed in a twisted (inverted) state at 180 ° C.

As a method for producing a inclined electrode having a Si material (Si alloy) ratio in the negative electrode, when preparing the negative electrode active material slurry, the solid content ratio (active material weight + conductive auxiliary agent weight + thickener) in the slurry is used. Weight + total weight of solids such as binder powder weight / slurry weight) is 35 to 45% by mass. By doing so, it becomes easy to reduce the viscosity of the slurry and give it a slope. After applying (coating) this slurry on a current collector (current collector foil), the slurry is dried in a low temperature environment of 40 to 90 ° C. with the coated surface facing down. By doing so, the Si material (Si alloy) is closer to the positive electrode facing surface side due to the relationship between the specific gravity of the Si material (Si alloy) active material particles and the carbon material active material particles, and the inclined electrode can be produced. In order to make the slurry more inclined, it is preferable that the solid content ratio in the slurry is 36 to 43% by mass and the drying temperature is in the range of 40 to 70 ° C. In addition to the above method, the drying time may be further changed for adjustment. Alternatively, three or more types having different solid content ratios in the negative electrode active material slurry may be prepared, coated and dried in this order to form a negative electrode active material layer having a laminated structure of three or more layers, which is particularly limited. It's not something.

The solvent is not particularly limited, and N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide, cyclohexane, hexane, water and the like can be used.

The method for applying the active material slurry to the current collector is not particularly limited, and examples thereof include a screen printing method, a spray coating method, an electrostatic spray coating method, an inkjet method, and a doctor blade method.

The method for drying the coating film formed on the surface of the current collector is not particularly limited, and at least a part of the solvent in the coating film may be removed. Examples of the drying method include heating. The drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the volatilization rate of the solvent contained in the active material slurry to be applied, the coating amount of the active material slurry, and the like. A part of the solvent may remain. The remaining solvent can be removed by a pressing step or the like described later.

The pressing means is not particularly limited, and for example, a calendar roll, a flat plate press, or the like can be used.

(2) Preparation of cell cell layer The cell cell layer can be produced by laminating the electrodes (positive electrode and negative electrode) produced in (1) via a separator (electrolyte layer).

(3) Production of Power Generation Element The power generation element can be produced by laminating the cell cell layers produced in (2) above, appropriately considering the output and capacity of the cell cell layer, the output and capacity required as a battery, and the like. ..

(4) Manufacture of laminated battery As the battery configuration, various shapes such as a square type, a paper type, a laminated type, a cylindrical type, and a coin type can be adopted. Further, the current collector, the insulating plate, and the like of the constituent parts are not particularly limited, and may be selected according to the above-mentioned shape. However, in this embodiment, a laminated battery is preferable. The laminated battery has leads bonded to the current collector of the power generation element obtained above, and these positive electrode leads or negative electrode leads are bonded to the positive electrode tab or the negative electrode tab. Then, a laminated battery is manufactured by putting a power generation element in a laminated sheet so that the positive electrode tab and the negative electrode tab are exposed to the outside of the battery, injecting an electrolytic solution with a liquid injection machine, and then sealing the battery in a vacuum. sell.

(5) Activation treatment, etc. In this embodiment, from the viewpoint of enhancing the performance and durability of the laminated battery obtained above, initial charging treatment, gas removal treatment, activation treatment, etc. are further required under the following conditions. It may be done according to. In this case, in the production of the laminated battery according to (4) above, the three sides of the laminated sheet (exterior material) are completely sealed by thermocompression bonding in a rectangular shape so that the gas can be removed. It is stopped (mainly sealed), and the remaining one side is temporarily sealed by thermocompression bonding. The remaining one side may be opened and closed by, for example, clipping, but from the viewpoint of mass production (production efficiency), it is preferable to temporarily seal by thermocompression bonding. In this case, it is only necessary to adjust the crimping temperature and pressure. When temporarily sealed by thermocompression bonding, it can be opened by applying a light force, and after degassing, it may be temporarily sealed by thermocompression bonding again, and finally it is completely sealed by thermocompression bonding ( This sealing) is sufficient.

(First charge processing)
The battery aging treatment (initial charging treatment) is preferably carried out as follows. At 25 ° C. (within ± 2.5 ° C.; atmospheric temperature; the same applies hereinafter), charging is performed at 0.05 C for 4 hours (about 20% SOC) by a constant current charging method. Then, after charging to 4.45 V at a rate of 0.1 C at 25 ° C., charging is stopped and held in that state (SOC about 70%) for about 2 days (48 hours).

(First (first) gas removal treatment)
Next, as the first (first) gas removal treatment, the following treatment is performed. First, one side temporarily sealed by thermocompression bonding is opened, gas is removed at 10 ± 3 hPa for 5 minutes, and then thermocompression bonding is performed again to perform temporary sealing. Further, the electrode and the separator are sufficiently brought into close contact with each other by pressurizing (surface pressure 0.5 ± 0.1 MPa) with a roller.

(Activation treatment)
Next, as the activation treatment method, the following electrochemical pretreatment method is performed.

First, the battery is charged at 25 ° C. by a constant current charging method at 0.1 C until the voltage reaches 4.45 V, and then discharged to 2.0 V at 0.1 C twice. Similarly, at 25 ° C., a cycle of charging to 4.55 V at 0.1 C by a constant current charging method and then discharging to 2.0 V at 0.1 C is performed once, and 4.65 V at 0.1 C. After charging until it becomes, a cycle of discharging to 2.0 V at 0.1 C is performed once. Further, at 25 ° C., a constant current charging method may be used to charge the battery to 4.75 V at 0.1 C and then discharge to 2.0 V at 0.1 C once.

Here, the constant current charging method is used as the activation processing method, and the electrochemical pretreatment method when the voltage is set as the termination condition is described as an example, but the charging method is the constant current constant voltage charging method. You may use it. Further, as the termination condition, the amount of electric charge or time may be used in addition to the voltage.

(Last (second) gas removal treatment)
Next, as the final (second) gas removal treatment, the following treatment is performed. First, one side temporarily sealed by heat crimping is opened, gas is removed at 10 ± 3 hPa for 5 minutes, and then heat crimping is performed again to perform main sealing. Further, the electrode and the separator are sufficiently brought into close contact with each other by pressurizing (surface pressure 0.5 ± 0.1 MPa) with a roller.

In the present embodiment, the performance and durability of the obtained battery can be improved by performing the above-mentioned initial charge treatment, gas removal treatment, and activation treatment.

[Battery set]
The assembled battery is configured by connecting a plurality of batteries. Specifically, it is composed of serialization, parallelization, or both by using at least two or more batteries. By connecting in series or in parallel, 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 invention, including the lithium ion secondary battery according to the present embodiment, maintains the discharge capacity even after long-term use and has good cycle characteristics. In addition, the volumetric energy density is high. 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 lithium ion secondary battery (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 invention, since a long-life battery having excellent long-term reliability and output characteristics can be configured, a plug-in hybrid electric vehicle having a long EV mileage and an electric vehicle having a long one-charge mileage can be configured by mounting such a battery. .. In addition to hybrid vehicles, fuel cell vehicles, electric vehicles (all four-wheeled vehicles (passenger cars, trucks, commercial vehicles such as 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 94% by mass of NMC composite oxide as positive electrode active material, 3% by mass of acetylene black as conductive aid, 3% by mass of polyvinylidene fluoride (PVDF) as binder, and N-methyl-, which is a slurry viscosity adjusting solvent. An appropriate amount of 2-pyrrolidone (NMP) was mixed 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 was formed on the back surface in the same manner to prepare a positive electrode having positive electrode active material layers formed on both sides of the positive electrode current collector (aluminum foil). The amount of one-sided coating of the positive electrode active material layer was 21 mg / cm ² (excluding foil). The density of the positive electrode active material layer was 3.0 g / cm ³ (excluding foil). The aspect ratio of the electrodes (the aspect ratio of the rectangular positive electrode active material layer) was 1.3.

The PVDF includes Kureha Battery Materials Japan Co., Ltd., Kureha KF polymer, powder type, grade No. W # 7200 was used. As the NMC composite oxide, _{one having a composition represented by LiNi 0.5} Mn _0.3 Co _0.2 O ₂ (average particle size 15 μm) was used. This was above general formula _{(1): Li a Ni b} Mn c Co d M Applying the _{x O 2, a = 1,} b = 0.5, c = 0.3, d = 0.2, x = Those having 0, b + c + d = 1 and satisfying the requirements of the general formula (1) were used. This NMC composite oxide was prepared by the following preparation method.

(Preparation of NMC composite oxide)
Sodium hydroxide and ammonia were continuously supplied at 60 ° C. to an aqueous solution (1 mol / L) in which nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved to adjust the pH to 11.3, and nickel was prepared by the coprecipitation method. And manganese and cobalt were dissolved at a molar ratio of 50:30:20 to prepare a metal composite hydroxide.

This metal composite hydroxide and lithium carbonate are weighed so that the ratio of the total number of moles of metals other than Li (Ni, Mn, Co) to the number of moles of Li is 1: 1 and then mixed sufficiently. The temperature is raised at a temperature rising rate of 5 ° C./min, tentatively fired at 900 ° C. for 2 hours in an air atmosphere, then heated at a temperature rising rate of 3 ° C./min, main fired at 920 ° C. for 10 hours, and cooled to room temperature. To obtain an NMC composite oxide which is a positive electrode active material having a composition of LiNi _0.5 Mn _0.3 Co _0.2 O _2. The secondary particle size (average particle size D50) of the obtained NMC composite oxide was 10 μm. As the secondary particle size (average particle size D50), the value obtained by the laser diffraction method was used (hereinafter, the same applies).

2. Fabrication of Negative Electrode Fabrication of Negative Electrode of Comparative Example 1-1 Natural graphite 76.8% by mass and Si—Ti alloy 19.2% by mass as negative electrode active material, carbon black 1% by mass as conductive aid, SBR 2% by mass as binder, and As a thickener, 1% by mass of an ammonium salt of CMC was prepared. These were added to purified water and stirred and mixed using a stirring defoamer for 4 minutes to prepare a negative electrode active material (aqueous) slurry which was sufficiently dispersed. The solid content ratio of the negative electrode active material (aqueous) slurry was adjusted to 46% by mass. The solid content ratio is the total weight (solid content) of the negative electrode active material Si-Ti alloy (Si material), natural graphite (carbon material), binder powder, conductive additive and thickener divided by the slurry weight. Indicates the percentage (mass%). Further, as the carbon black, Super-P (registered trademark) manufactured by IMERYS (with an average particle size (secondary particle size) D50 of 40 nm) was used. Further, styrene-butadiene rubber latex was used as the binder so that the solid content of styrene-butadiene rubber (SBR) in the binder was 2% by mass. The ammonium salt of CMC, which is a thickener, is an abbreviation for the ammonium salt of carboxymethyl cellulose. As the natural graphite which is the carbon material of the negative electrode active material, one having an average particle diameter (secondary particle diameter) D50 of 20 μm was used. Further, as the Si—Ti alloy which is the Si material (Si alloy) of the negative electrode active material, the one obtained by the following synthesis method was used.

(Synthesis of Si-Ti alloy)
As the Si—Ti alloy, _{an alloy having a composition represented by Si 90} Ti ₁₀ (unit: mass%) was used. This Si—Ti alloy was manufactured (prepared) by the mechanical alloy method. Specifically, using a planetary ball mill device P-6 manufactured by Fritsch of Germany, zirconia crushed balls and raw material powder of alloy were put into a zirconia crushed pot and alloyed at 450 rpm for 48 hours (alloying treatment). ), 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. The average particle size (secondary particle size) D50 of the obtained Si—Ti alloy powder was 2 μm. Here, the alloying treatment is to alloy by applying high energy to the raw material powder of the alloy at a high rotation speed (450 rpm). 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 average particle size D50 of the obtained Si—Ti alloy powder was 2 μm.

The above negative electrode active material (water-based) slurry is applied to a copper foil (thickness 10 μm) serving as a negative electrode current collector, dried at 120 ° C. for 10 minutes, and then compression-molded with a roll press to form a negative electrode active material having a rectangular planar shape. Layers were made. A negative electrode active material layer was formed on the back surface in the same manner to prepare a negative electrode having negative electrode active material layers formed on both sides of the negative electrode current collector (copper foil). The amount of one-sided coating of the negative electrode active material layer was 7.6 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 with the positive electrode facing the positive electrode, which will be described later, was 1.20. The thickness of the negative electrode active material layer (one side) was 55 μm. The density of the negative electrode active material layer was 1.6 g / cm ³ (excluding foil). Here, the A / C ratio refers to the capacity ratio of the negative electrode (Anode) capacity (Li acceptance amount) and the positive electrode (Cathode) capacity (Li discharge amount). That is, the A / C ratio is the ratio of the Li acceptance amount (capacity) of the negative electrode and the Li discharge amount (capacity) of the positive electrode. In addition, these capacity ratios were designed based on the measured capacities measured by the half cell. The density of the negative electrode active material layer was 1.6 g / cm ³ (excluding foil). Further, when the negative electrode active material layer is applied to the formula (1) of α (Si material) + β (carbon material), the Si material is a Si—Ti alloy, the carbon material is natural graphite, and α + β = 96, α = 19.2 and β = 76.8, satisfying the requirement of equation (1).

Preparation of Negative Electrode of Comparative Example 1-2 In Comparative Example 1-1, the same as in Comparative Example 1-1 except that the solid content ratio of the slurry was 43% by mass and the drying temperature after coating was 30 ° C. A negative electrode was prepared. The density of the negative electrode active material layer was 1.6 g / cm ³ (excluding foil).

Preparation of Negative Electrodes of Comparative Example 1-3 In Comparative Example 1-1, the comparison was made except that the solid content ratio of the slurry was 38% by mass, the coated surface was facing down after coating, and the slurry was dried at 60 ° C. A negative electrode was prepared in the same manner as in Example 1-1. The density of the negative electrode active material layer was 1.6 g / cm ³ (excluding foil).

Preparation of Negative Electrode of Example 1-1 In Comparative Example 1-1, comparison was made except that the solid content ratio of the slurry was 43% by mass, the coated surface was facing down after coating, and the slurry was dried at 60 ° C. A negative electrode was prepared in the same manner as in Example 1-1. The density of the negative electrode active material layer was 1.6 g / cm ³ (excluding foil).

Preparation of Negative Electrode of Example 1-2 In Comparative Example 1-1, the comparison was made except that the solid content ratio of the slurry was 41% by mass, the coated surface was facing down after coating, and the slurry was dried at 40 ° C. A negative electrode was prepared in the same manner as in Example 1-1. The density of the negative electrode active material layer was 1.6 g / cm ³ (excluding foil).

3. 3. Preparation of Battery The positive electrode obtained in 1 above and the negative electrode obtained in 2 above were cut out so as to have an active material layer area of 4 cm in length × 3 cm in width, and a porous polypropylene separator (thickness 25 μm, porosity 55%). ) (1 positive electrode, 2 negative electrodes) to produce a power generation element. 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 a positive electrode current collector plate or a negative electrode current collector plate. 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 plate and the negative electrode current collector plate are exposed to the outside of the battery, and the liquid is injected. The electrolytic solution was injected through the opening by the machine. This aluminum laminated sheet bag is made by stacking two aluminum laminated sheets (a film sheet made by laminating aluminum with a film containing polypropylene) and sealing three of the four outer circumferences (outer edges) by thermocompression bonding. It is (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 weight of the solution. The one to 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 plate and the negative electrode current collector plate connected to both electrodes (current collectors) via leads are led out. Then, a test cell, which is a laminated lithium-ion secondary battery, was completed. The rated capacity of the battery at this time is as follows in 4.2. From the measurement result of the rated capacity, it was 80 mAh (0.080 Ah).

4. Battery evaluation 4.1. Evaluation of Battery Characteristics The rated capacity of each battery (test cell) obtained above was measured by performing a charge / discharge test under the following conditions, and the cycle durability was further evaluated.

4.2. Measurement of rated capacity The rated capacity of the battery (test cell) was calculated as follows.

The rated capacity of the battery (test cell) is about 10 hours after injecting the electrolytic solution, and then the temperature is 25 ° C (within ± 2.5 ° C; atmospheric temperature), 3.0 V to 4 Measured in the voltage range of .15 V by the following steps 1-5.

Step 1: After reaching 4.15V with a constant current charge of 0.1C, it was rested for 5 minutes.

Step 2: After step 1, the battery was charged by constant voltage charging for 1.5 hours and rested for 5 minutes.

Step 3: After reaching 3.0 V by constant current discharge of 0.1 C, it was discharged by constant voltage discharge for 2 hours, and then paused for 10 seconds.

Step 4: After reaching 4.1 V by constant current charging at 0.1 C, the battery was charged by constant voltage charging for 2.5 hours, and then paused for 10 seconds.

Step 5: After reaching 3.0 V by constant current discharge of 0.1 C, it was discharged by constant voltage discharge for 2 hours, and then stopped for 10 seconds.

Rated capacity: The discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in step 5 was defined as the rated capacity.

4.3. Cycle durability evaluation In the cycle durability evaluation, the above 3. For each battery (test cell) obtained in the production of the battery, charging / discharging at a 0.5 C rate was repeated at 25 ° C. (within ± 2.5 ° C.; the same applies hereinafter) for 100 cycles. At the time of evaluation of the battery, the charging condition was the constant current constant voltage charging method until the maximum voltage became 4.2 V at a rate of 0.5 C and then the current value became 0.01 C. 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). The ratio of the discharge capacity in the 100th cycle to the discharge capacity in the 1st cycle was evaluated as a "capacity retention rate (%)". The obtained results are shown in the column of "maintenance rate (%) @ 100cyc" in Table 1 below.

4.4. Measurement of the inclined electrode structure of the negative electrode active material layer (when the in-plane central part (1 point) is selected as the measurement point in the negative electrode active material layer surface, the cross section of the negative electrode active material layer is evenly divided into three in the electrode thickness direction. (Calculation method of the ratio of the area of Si material in each divided area)
Above 3. A negative electrode (length 4 cm x width 3 cm) was prepared in the same manner as in the production of the battery. Using the cross-section polisher method as a cross-section processing method for this negative electrode, the sample is irradiated with an argon ion beam, and the sample is scraped using the sputtering phenomenon that flicks off the sample atoms. The cross section was processed along the direction. After that, for one location (one image data) of the negative electrode cross section; central portion (image size; horizontal (in-plane direction) 100 μm × vertical (thickness direction) 70 μm; including the negative electrode active material layer portion on one side). A reflected electron image was imaged with an electron microscope (SEM) (see FIG. 4 (a)). The SEM image (reflected electron image) is binarized using image processing software (WinROOF manufactured by Mitani Shoji) to grayscale the image, and then grayscale the Si material part and parts other than the Si material part. A processed image (see FIG. 4B) in which a threshold was set between the values was obtained. With respect to such a processed image, the cross section of the negative electrode active material layer was evenly divided into three in the electrode thickness direction, and the area amount of the Si material portion within each divided area was determined. Then, the ratio of the area of the Si material portion to the total area of each divided image (the area of the Si material / the area of the entire image × 100 (%)) was calculated. As a method of setting the above threshold value, an intermediate value between the numerical values of the Si material and the material other than the Si material portion was set as the threshold value. Note that FIG. 4A is a drawing showing a reflected electron image (measurement image) taken by an electron microscope (SEM) of the negative electrode of Comparative Example 1-1, and FIG. 4B is FIG. 4A. It is a drawing in which the measurement image of No. 1 is grayscaled by binarization processing (the white part in the figure corresponds to the Si material part). Further, in FIG. 4B, the cross section of the negative electrode active material layer is evenly divided into three in the thickness direction for the processed image, and the cross sections (divided sections) divided into three are collected from the positive electrode facing surface (surface; separator) side. The symbols A, B, and C are attached in order toward the electric body side. When the cross section of the negative electrode active material layer is evenly divided into three in the thickness direction, and when the entire cross section of the negative electrode active material layer in the electrode thickness direction is 100%, the ratio (division ratio) of each divided cross section is 33.3. It is in the range of% ± 0.3% (preferably ± 0.1%), and the total may be 100%.

Specifically, the result of the negative electrode cross-section SEM (the SEM image (see FIG. 4A)) is binarized and grayscaled, the threshold value is set, and the processed image (see FIG. 4B). The cross section of the negative electrode active material layer (one side thickness 55 μm) not including the current collector on one side was evenly divided into three in the thickness direction with respect to this processed image. Then, within each divided area. The ratio (%) of the area of the Si material in the above was calculated (using the above image processing software). In Table 1, the cross section (divided section) divided into three is divided into three from the positive electrode facing surface (surface) side to the current collector side. A, B, and C are set in order toward the above (corresponding to A, B, and C attached to the three-divided cross section (divided section) in FIG. 4 (b)).

From the results in Table 1, as shown in Example 1-1, in the inclined electrode in which the mixing ratio of the Si material increases from the current collector side (section C) to the positive electrode facing surface side (section A), Comparative Example 1- Compared with the electrode without inclination shown in No. 1, a significant improvement effect was confirmed in the discharge capacity retention rate. This is because there are few Si materials with large volume changes near the current collector, so damage to the current collector and peeling of the negative electrode active material layer are reduced, and electron conductivity is maintained during the charge / discharge process. Seem. Further, as shown in Example 1-2, when the rate of increase in inclination (the rate at which the area (ratio) of the Si material increases between the sections from A to C) is as large as 5% or more, the durability is durable. Further improvement in sexuality was confirmed, and it is considered that the above effects were further exerted.

Further, as shown in Comparative Example 1-2, a decrease in durability is observed in the inclined electrode in which the mixing ratio of the Si material decreases from the current collector side (division section C) to the positive electrode facing surface side (division section A). Was done. This is because there are many Si materials with large volume changes near the current collector, which causes peeling of the negative electrode active material layer and deformation of the current collector near the current collector, resulting in large loss of the active material and reduced durability. It seems that it was done.

Further, as shown in Comparative Example 1-3, when the rate of increase in the inclination was as high as 15 to 16% (more than 12%), a decrease in durability was observed. It is considered that this is because the rate of increase is too high and the rate of change in volume in the ABC division (block) is too large, so that peeling occurs between the blocks.

From the above, as in the present embodiment, the volume changes in the vicinity of the current collector by using the inclined electrode in which the mixing ratio of the Si material increases by an appropriate amount (1 to 12%) from the current collector side to the positive electrode facing surface side. Since there are few Si materials with a large volume, damage to the current collector and peeling of the active material layer are reduced. As a result, it was confirmed that by maintaining the electron conductivity in the charge / discharge process, high capacity can be maintained, the discharge capacity retention rate can be significantly improved, and both capacity and cycle durability can be achieved at the same time. did it.

10,50 Lithium-ion secondary battery,
11, 31 Negative current collector,
12 Positive electrode current collector,
13, 33 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,
30 negative electrode,
33a coating film (coating film),
35 Si material (Si alloy) active material particles,
37 Carbon Material Active Material Particles,
58 Positive tab,
59 Negative electrode tab.

Claims (7)

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 layer has the following formula (1).

(In the formula, the Si material is a material made of an alloy containing Si, and α and β represent the mass% of each component in the negative electrode active material layer, 80 ≦ α + β ≦ 98, 0.1 ≦ α ≦ 40, 58 ≦ β ≦ 97.9), and contains a negative electrode active material.
When an arbitrary location is selected in the surface of the negative electrode active material layer, when the cross section of the negative electrode active material layer is evenly divided into three in the electrode thickness direction, the area of the Si material in each divided area is the current collection. From the body side to the positive electrode facing surface side, the amount increases by 1% or more and 12% or less, and the negative electrode active material layer is evenly divided into three in the electrode thickness direction, and the region on the current collector side, the intermediate region, and the positive electrode facing surface side. The negative electrode for a non-aqueous electrolyte secondary battery, characterized in that the density of the region on the positive electrode facing surface side is higher than the density of the region on the current collector side. The negative electrode according to claim 1 and
A positive electrode having a current collector and a positive electrode active material layer containing a positive electrode active material arranged on the surface of the current collector,
Separator and
A non-aqueous electrolyte secondary battery characterized by having a power generation element including. The positive electrode active material, the general formula _{(1): Li a Ni b} Mn c Co d M x O 2 ( where, a, b, c, d, x is, 0.9 ≦ a ≦ 1.2,0 < b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, b + c + d = 1 are satisfied, and M is Ti, Zr, Nb, W, P, Al, Mg. The non-aqueous electrolyte secondary battery according to claim 2 , wherein the non-aqueous electrolyte secondary battery comprises a lithium nickel-based composite oxide represented by (at least one selected from the group consisting of V, Ca, Sr and Cr). The non-aqueous electrolyte secondary battery according to claim 2 or 3 , wherein the separator is a separator in which a heat-resistant insulating layer is laminated on a porous substrate. Claims 2 to 4 characterized in that the value of the ratio of the battery volume (the product of the projected area and the thickness of the battery including the battery exterior) to the ^{rated capacity is 10 cm 3} / Ah or less, and the rated capacity is 3 Ah or more. The non-aqueous electrolyte secondary battery according to any one of the above items. The invention according to any one of claims 2 to 5 , wherein the electrode shape is rectangular, and the aspect ratio of the electrode defined as the aspect ratio of the rectangular electrode active material layer is 1 to 4. Non-aqueous electrolyte secondary battery. The non-aqueous electrolyte according to any one of claims 2 to 6 , wherein the flat laminated laminated battery has a structure in which the power generation element is enclosed in a battery outer body made of a laminated film containing aluminum. Secondary battery.

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