JP2019145457A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

To provide a non-aqueous electrolyte secondary battery in which suppression of heat generation due to charging/discharging and improvement of high rate cycle characteristics are compatible.SOLUTION: A non-aqueous electrolyte secondary battery includes a positive electrode 30, a negative electrode 50, a separator 40, an inorganic filler layer 20 disposed between the negative electrode 50 and the separator 40, and a non-aqueous electrolyte. The inorganic filler layer 20 includes a first layer 21 disposed on the negative electrode 50 side, and a second layer 22 disposed adjacent to the first layer 21 and disposed on the separator 40 side. When the porosity of the first layer 21 is represented by S1 and the porosity of the second layer 22 is represented by S2, S1 and S2 satisfy relationships of S1≥S2 and 53<S1≤77.1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention relates to a non-aqueous electrolyte secondary battery including an inorganic filler layer between a negative electrode and a separator.

  A non-aqueous electrolyte secondary battery represented by a lithium ion battery is preferably used as a portable power source, a high output power source for mounting on a vehicle, and the like because it is lightweight and has a high energy density. For example, in a non-aqueous electrolyte secondary battery used for high output, it is made of an inorganic filler having heat resistance between the electrode and the separator for the purpose of preventing a short circuit due to thermal contraction of the separator during overcharge. What is provided with the inorganic filler layer is known (for example, refer patent document 1 etc.). For example, Patent Document 1 discloses that the inorganic filler layer has a density (corresponding to a filling rate) of 40% or more and 95% or less so that the ionic conductivity between the positive and negative electrodes is adjusted to an appropriate range while the inorganic filler layer is adjusted to an appropriate range. It is disclosed that the strength and bonding strength of the filler layer can be kept strong.

International Publication No. 09/081594

By the way, a secondary battery that is charged and discharged at a high output and at a high rate is characterized in that the battery easily generates heat even during normal use (charging and discharging). Therefore, when the battery is repeatedly charged and discharged at a high output and at a high rate, the heat generated in the battery is accumulated and the battery tends to fall into an overcharge state, or the temperature rise at the time of a short circuit is easily accelerated. In another aspect, a battery that is repeatedly charged and discharged at a high output and at a high rate has a problem that the concentration of the nonaqueous electrolytic solution becomes uneven as the cycle proceeds, and the resistance increases.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery in which suppression of heat generation due to charging / discharging and improvement of high rate cycle characteristics are compatible. Objective.

  In order to solve the above problems, the present invention provides a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, an inorganic filler layer disposed between the negative electrode and the separator, and non-water And a non-aqueous electrolyte secondary battery comprising the electrolyte solution. Here, the inorganic filler layer includes a first layer disposed on the negative electrode side and a second layer disposed adjacent to the first layer and disposed on the separator side. When the porosity of the first layer is represented by S1 and the porosity of the second layer is represented by S2, the relationship between S1 and S2 is as follows: S1 ≧ S2; and 53 <S1 ≦ 77.1. Fulfill. With such a configuration, when the secondary battery is repeatedly charged and discharged at a high rate, the amount of heat generated by the battery can be reduced, and an increase in resistance can be suppressed. In other words, a secondary battery that achieves both safety and high-rate cycle resistance is realized.

  In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, both the first layer and the second layer include two or more kinds of fillers having different average aspect ratios. By this, the 1st layer and the 2nd layer can be constituted using the same material, and the continuity with the 1st layer and the 2nd layer can be realized simply and suitably.

  In one preferable example, the inorganic filler layer includes a first filler and a second filler having different average aspect ratios, and the average aspect ratio of the first filler is twice or more the average aspect ratio of the second filler. . Such a configuration is preferable because the electrolyte solution easily penetrates into the inorganic filler layer.

  In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, both the first layer and the second layer include two or more kinds of fillers having different average major axes. Accordingly, the porosity can be easily and suitably adjusted while using the same material for the first layer and the second layer.

  In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the first layer is formed so as to be directly bonded to the surface of the negative electrode. The inorganic filler layer disclosed here is designed to be higher than ever, with the porosity S1 of the first layer in contact with the negative electrode exceeding 53%. Therefore, even when the inorganic filler layer is directly formed on the surface of the negative electrode, inhibition of the occlusion and release of charge carriers on the negative electrode surface is suitably suppressed.

  The above non-aqueous electrolyte secondary battery can be provided as a battery that can suitably suppress an increase in resistance when repeatedly charged and discharged at a high rate and has high safety. Therefore, taking advantage of such characteristics, it can be suitably used as a power source (driving power source) for a hybrid vehicle or a plug-in hybrid vehicle.

It is a figure which shows typically the cross-sectional structure of the nonaqueous electrolyte secondary battery which concerns on one Embodiment. It is a schematic diagram explaining the permeation | transmission path | route of a non-aqueous electrolyte when mixing (a) two types of granular fillers, and (b) mixing a granular and plate-shaped filler. It is the graph which illustrated the relationship between the mixing ratio when two types of fillers were mixed, and the porosity. It is the figure which illustrated the relationship between the average porosity of an inorganic filler layer, and the emitted-heat amount. It is the figure which illustrated the relationship between the average porosity of the 1st layer of an inorganic filler layer, and the emitted-heat amount. It is the figure which illustrated the relationship between the average porosity of an inorganic filler layer, and electrolyte solution penetration time. It is the figure which illustrated the relationship between the average porosity of the 1st layer of an inorganic filler layer, and electrolyte solution penetration time. It is the figure which illustrated the relationship between the average porosity of the 2nd layer of an inorganic filler layer, and electrolyte solution penetration time.

  Hereinafter, an embodiment of the non-aqueous electrolyte secondary battery disclosed herein will be described. It should be noted that matters other than matters specifically mentioned in the present specification (for example, the structure of the inorganic filler layer, etc.) and matters necessary for the implementation of the present invention (for example, the structure of the secondary battery that does not characterize the present invention) And the manufacturing process etc. can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In addition, dimensional relationships (length, width, thickness, etc.) in the drawings shown below do not necessarily reflect actual dimensional relationships. In this specification, the notation “X to Y” indicating a numerical range means “X or more and Y or less”.

  In the present specification, the “non-aqueous electrolyte secondary battery” refers to a battery that can be repeatedly charged and discharged using a non-aqueous electrolyte solution containing electrolyte ions as an electrolyte. For example, a secondary battery that uses lithium ions (Li ions) as the electrolyte ions and is charged and discharged by the movement of charges accompanying Li ions between the positive and negative electrodes is included. A battery generally called a lithium ion battery or a lithium secondary battery is a typical example included in the non-aqueous electrolyte secondary battery in this specification. Hereinafter, the technique disclosed herein will be described using a case where the nonaqueous electrolyte secondary battery is a lithium ion battery as an example.

[Nonaqueous electrolyte secondary battery]
FIG. 1 is a schematic cross-sectional view showing a configuration of a non-aqueous electrolyte secondary battery 10 disclosed herein. The non-aqueous electrolyte secondary battery 10 includes a positive electrode 30, a negative electrode 50, an inorganic filler layer 20, a separator 40, and a non-aqueous electrolyte (not shown). Each component will be described below.

The negative electrode 50 is configured by including a negative electrode active material layer 54 on a negative electrode current collector 52. The negative electrode active material layer 54 includes a negative electrode active material. Typically, the particulate negative electrode active material may be bonded to each other by a binder (binder) and bonded to the negative electrode current collector 52. As the negative electrode active material, various materials conventionally used as a negative electrode active material for lithium ion secondary batteries can be used without any particular limitation. Preferred examples include carbon-based materials typified by artificial graphite, natural graphite, amorphous carbon, and composites thereof (for example, amorphous carbon-coated graphite), or materials that form an alloy with lithium such as silicon (Si). Lithium alloy (for example, Li _X M, M is C, Si, Sn, Sb, Al, Mg, Ti, Bi, Ge, Pb, P, etc., X is a natural number), silicon compound (SiO, etc.) And lithium storable compounds such as The negative electrode 50 includes, for example, a powdered negative electrode active material and a binder (for example, rubber such as styrene-butadiene copolymer (SBR), acrylic acid-modified SBR resin (SBR latex), carboxymethyl cellulose (CMC), and the like. A negative electrode paste prepared by dispersing a cellulose-based polymer or the like in a suitable dispersion medium (for example, water or N-methyl-2-pyrrolidone, preferably water) on the surface of the negative electrode current collector 52, and then drying. Then, it can be produced by removing the dispersion medium. As the negative electrode current collector, a conductive member made of a metal having good conductivity (for example, copper, nickel, titanium, stainless steel, etc.) can be suitably used.

The average particle diameter (D ₅₀ ) of the negative electrode active material particles is not particularly limited, and is, for example, 0.5 μm or more and 50 μm or less, preferably 1 μm or more and 40 μm or less, and more preferably 5 μm or more and 30 μm or less. The average particle size in this specification is a cumulative 50% particle size in a volume-based particle size distribution determined by a laser diffraction light scattering method, unless otherwise specified. The proportion of the negative electrode active material in the entire negative electrode active material layer 54 is suitably about 50% by mass or more, and preferably 90% by mass to 99% by mass, for example, 95% by mass to 99% by mass. When a binder is used, the proportion of the binder in the negative electrode active material layer 54 can be set to, for example, 1 part by mass to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material, and usually about 1 part by mass to 5 parts by mass is appropriate. The thickness and density of the negative electrode active material layer 54 can be adjusted by appropriately pressing the negative electrode. The thickness (average thickness, the same applies hereinafter) of the negative electrode active material layer 54 after the press treatment is, for example, 20 μm or more, typically 50 μm or more, and is 300 μm or less, typically 200 μm or less, for example, 100 μm or less. It can be. Further, the density of the negative electrode active material layer 54 is not particularly limited, but is, for example, 0.8 g / cm ³ or more, typically 1.0 g / cm ³ or more, and 1.6 g / cm ³ or less, typically May be 1.5 g / cm ³ or less, for example 1.4 g / cm ³ or less. Moreover, the porosity of the negative electrode active material layer 54 is, for example, 22 to 55%.

The positive electrode 30 is configured by including a positive electrode active material layer 34 on a positive electrode current collector 32. The positive electrode active material layer 34 includes a positive electrode active material. Typically, the particulate positive electrode active material may be bonded to the positive electrode current collector 32 while being bonded together with a conductive material by a binder (binder). As the positive electrode active material, various materials conventionally used as the positive electrode active material of lithium ion secondary batteries can be used without any particular limitation. As a suitable example, lithium nickel oxide (for example, LiNiO ₂ ), lithium cobalt oxide (for example, LiCoO ₂ ), lithium manganese oxide (for example, LiMn ₂ O ₄ ), and a composite thereof (for example, LiNi _0.5 Mn _{1) .5} O ₄ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) or other oxide particles (lithium transition metal oxide) containing lithium and a transition metal element as constituent metal elements, phosphoric acid Examples thereof include phosphate particles containing lithium and a transition metal element as constituent metal elements, such as manganese lithium (LiMnPO ₄ ) and lithium iron phosphate (LiFePO ₄ ). Such a positive electrode 30 includes, for example, a positive electrode active material, a conductive material, and a binder (for example, an acrylic resin such as a methacrylate polymer, a halogenated vinyl resin such as polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), and the like. A positive electrode paste prepared by dispersing the polyalkylene oxide and the like in a suitable dispersion medium (for example, N-methyl-2-pyrrolidone) on the surface of the positive electrode current collector 32, and then drying to remove the dispersion medium. Can be produced. As the positive electrode current collector 32, a conductive member made of a metal having good conductivity (for example, aluminum, nickel, titanium, stainless steel, etc.) can be suitably used. As the conductive material, for example, carbon materials such as carbon black (typically acetylene black and ketjen black), activated carbon, graphite, and carbon fiber can be suitably used.

The average particle diameter (D ₅₀ ) of the positive electrode active material particles is not particularly limited, and is, for example, 0.05 μm to 20 μm, preferably 0.5 μm to 15 μm, and more preferably 1 μm to 12 μm. The proportion of the positive electrode active material in the entire positive electrode active material layer 34 is suitably about 50% by mass or more, typically 50% by mass to 95% by mass, and usually about 70% by mass to 90% by mass. % Or less. The proportion of the conductive material in the positive electrode active material layer 34 can be, for example, approximately 0.1 parts by mass to 20 parts by mass with respect to 100 parts by mass of the positive electrode active material, and is usually approximately 1 part by mass to 15 parts by mass. For example, it is preferable to set it as 2 mass parts-10 mass parts, typically 3 mass parts-7 mass parts. The proportion of the binder in the positive electrode active material layer 34 can be, for example, approximately 0.5 parts by mass to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material, and is usually approximately 1 part by mass to 8 parts by mass. For example, it is preferably 2 to 7 parts by mass, typically 2 to 5 parts by mass. The thickness of the positive electrode active material layer 34 (average thickness; the same applies hereinafter) is, for example, 20 μm or more, typically 50 μm or more, and 300 μm or less, typically 200 μm or less, for example, 100 μm or less. be able to. The density of the positive electrode active material layer 34 is not particularly limited, but is, for example, 2 g / cm ³ or more, typically 2.5 g / cm ³ or more, and 4 g / cm ³ or less, typically 3.6 g. / Cm ³ or less. The positive electrode active material layer 34 satisfying the above range can realize high battery performance (for example, high energy density and output density). The porosity of the positive electrode active material layer 34 is, for example, 15 to 60%.

  The separator 40 is a constituent material that insulates the positive electrode active material layer 34 and the negative electrode active material layer 54 and provides a transfer path for charge carriers between the positive electrode active material layer 34 and the negative electrode active material layer 54. Such a separator 40 is typically disposed between the positive electrode 30 and the negative electrode 50. The separator 40 may have a non-aqueous electrolyte holding function described later and a shutdown function for closing the charge carrier movement path at a predetermined temperature. Such a separator 40 can be suitably constituted by a microporous resin sheet made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide. Among these, a microporous sheet made of a polyolefin resin such as PE or PP preferably has a shutdown temperature set within a range of 80 ° C to 140 ° C (typically 110 ° C to 140 ° C, for example, 120 ° C to 135 ° C). It is preferable because it is possible. The shutdown temperature is a temperature at which the electrochemical reaction of the battery is stopped when the battery generates heat, and the shutdown is typically expressed by melting or softening the separator 40 at this temperature. The separator 40 may have a single layer structure made of a single material, and two or more kinds of microporous resin sheets having different materials and properties (for example, average thickness, porosity, etc.) are laminated. It may be a structure (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer).

  The thickness of the separator 40 (average thickness; the same applies hereinafter) is not particularly limited, but is usually 5 μm or more, typically 10 μm or more, for example, 15 μm or more. The upper limit may be 40 μm or less, typically 30 μm or less, for example, 25 μm or less. When the average thickness of the substrate is within the above range, the charge carrier permeability can be kept good, and a minute short circuit (leakage current) is less likely to occur. For this reason, input / output density and safety can be achieved at a high level. Moreover, the porosity of the separator 40 is 30 to 60%, for example.

In the technique disclosed herein, the inorganic filler layer 20 is provided between the negative electrode 50 and the separator 40. The inorganic filler layer 20 is a porous insulating layer having heat resistance. The inorganic filler layer 20 has a porous structure that allows permeation of charge carriers, and has a heat resistance against a shutdown temperature (typically 80 ° C. to 140 ° C.) that stops the electrochemical reaction of the battery when the battery generates heat. Have sex. For example, a suitable example of the inorganic filler layer 20 is typically a layer composed of an inorganic filler and a binder. As the binder, for example, a binder that can be used for the positive and negative active material layers can be preferably used. As the inorganic filler, use a material having heat resistance sufficient to maintain insulation between the positive and negative electrodes without being softened or melted at a temperature of 600 ° C. or higher, typically 700 ° C. or higher, for example, 900 ° C. or higher. Can do. Specifically, it can be constituted by an inorganic material having the above heat resistance and insulation, a glass material, a composite material thereof, and the like. Typically, inorganic materials such as alumina (Al ₂ O ₃ ), magnesia (MgO), silica (SiO ₂ ), titania (TiO ₂ ), etc., which have various shapes that are roughly granular, plate-like, or fibrous. Oxides, nitrides such as aluminum nitride and silicon nitride, metal hydroxides such as calcium hydroxide, magnesium hydroxide and aluminum hydroxide, clay minerals such as mica, talc, boehmite, zeolite, apatite and kaolin, glass materials, etc. Is mentioned. Among them, alumina (Al ₂ O ₃ ), boehmite (Al ₂ O ₃ .H ₂ O), silica (SiO ₂ ), etc., which are stable in quality and inexpensive and easily available, are used as inorganic fillers. preferable.

The shape of the inorganic filler is not particularly limited. For example, for an inorganic filler powder that can be regarded as roughly granular (meaning nearly spherical here) having an average aspect ratio of less than 2, the average particle diameter may be 0.01 μm or more, and 0.1 μm or more is more preferable. Preferably, it may be 10 μm or less, for example, 5 μm or less. For example, for an inorganic filler powder having an anisotropy with an average aspect ratio of 2 or more (herein, meaning including needle shape or plate shape), for example, the average minor axis is 0.01 μm or more. It is preferably 0.1 μm or more, more preferably 2 μm or less, for example 1 μm or less. The average major axis may be 0.02 μm or more, more preferably 0.2 μm or more, and particularly preferably 0.5 μm or more. The upper limit of the average major axis is not particularly limited for the needle-like inorganic filler, and may be, for example, 100 μm or less. The upper limit of the average major axis of the plate-like inorganic filler may be, for example, 7 μm or less, preferably 5 μm or less, and more preferably 3 μm or less.
In addition, the average aspect-ratio of the inorganic filler in this specification is an arithmetic average value of the aspect-ratio about 100 or more inorganic filler particles calculated based on microscopic observation. Further, the aspect ratio is a value obtained as a major axis / minor axis. The major axis and minor axis are the dimensions of the long side and the short side of the circumscribed rectangle of the target particle, and are similarly measured based on microscopic observation.

The inorganic filler layer 20 includes a first layer 21 disposed on the negative electrode 50 side and a second layer 22 disposed on the separator 40 side. The first layer 21 and the second layer 22 are integrally joined adjacent to each other. Here, when the porosity (volume%) of the first layer 21 is represented by S1, and the porosity (volume%) of the second layer 22 is represented by S2, S1 and S2 satisfy the following relationship.
S1 ≧ S2
53 <S1 ≦ 77.1

  In other words, the porosity S1 of the first layer 21 is the same as or larger than the porosity S2 of the second layer 22. When S1> S2, a layer having a higher porosity is disposed on the negative electrode 50 side. Even when the porosity S1 and S2 of the first layer 21 and the second layer 22 are the same, the inorganic filler layer 20 has a two-phase structure, so that the first layer 21 and the second layer 22 are substantially the same. Smooth movement of the non-aqueous electrolyte between the layers 22 can be inhibited. As a result, more non-aqueous electrolyte can be secured on the surface of the negative electrode 50, and an increase in resistance can be suppressed even when high-rate charge / discharge is repeated. The ratio of the porosity S1 and S2 (S1 / S2) is preferably 1.05 or more, more preferably 1.1 or more, further preferably 1.2 or more, and may be 1.25 or more or 1.3 or more. . However, considering the practical mechanical strength of the first layer 21 and the effect of suppressing heat generation during overcharge, the ratio (S1 / S2) is preferably about 1.4 or less.

  More specifically, the porosity S1 of the first layer 21 is preferably higher than 53%. When the porosity S1 of the first layer 21 is in the range of 53% or less, movement of electrolyte ions can be hindered when charging and discharging are repeated at a high rate, which is not preferable. The porosity S1 of the first layer 21 is preferably 55% or more, more preferably 60% or more, and particularly preferably 65% or more. Further, if the porosity S1 of the first layer 21 exceeds 77.1% and becomes excessively large, the effect of suppressing heat generation at the initial stage of the short circuit is rapidly reduced, which is not preferable. According to the study by the present inventors, when the porosity S1 is in the range of approximately 77.1% or less, the porosity S1 and the amount of heat generated at the initial short circuit have a substantially linear correlation. Further, it is considered that the porosity S1 of the first layer 21 is preferably less than 82%. However, from the viewpoint of safety, it is preferably 77.1% or less, for example, 75% or less.

  As described above, the porosity S2 of the second layer 22 may be equal to or less than the porosity S1 of the first layer 21, and is preferably smaller than the porosity S1 of the first layer 21. For example, the porosity S2 of the second layer 22 may be 75% or less, may be 74% or less, and may be 70% or less, for example. On the other hand, if the porosity S2 of the second layer 22 is too low, the movement of electrolyte ions can be hindered when repeatedly charging and discharging at a high rate, which is not preferable. For example, the porosity S2 of the second layer 22 is preferably higher than 53%, preferably 55% or higher, and may be 60% or higher.

In addition, the value measured based on the Archimedes method can be employ | adopted for the porosity about the inorganic filler layer 20 in this specification, for example. Or as a porosity about the inorganic filler layer 20, you may employ | adopt the porosity of the inorganic filler used in order to form the inorganic filler layer 20 as follows. Here, the porosity S _R of the inorganic filler, the following _{formula: S R (%) = ×} 100 ( true specific gravity of 1-inorganic filler tap bulk density / inorganic filler) which is a value calculated based on. When using a mixed powder in which inorganic filler powders of a plurality of compositions are mixed as the inorganic filler, the bulk density and true specific gravity in the above formula are the bulk density of the mixed powder and the true density of each powder to be mixed. The theoretical true specific gravity obtained by multiplying the specific gravity by the mixing ratio may be adopted. In addition, said tap bulk density can be measured based on JIS R1628: 1997. Moreover, when an inorganic filler is a purchased item, you may employ | adopt a nominal value as a tap bulk density. Alternatively, it may be a porosity value calculated based on the space ratio estimation method from the tap bulk density of each powder to be mixed, the mixing ratio, the shape index of the powder, and the like. As the space ratio estimation method, various known methods can be adopted. As an example of the general-purpose method, for example, the methods described in the following documents can be appropriately adopted according to the properties of the powder.
“Estimation of spatial fraction of three-component spherical particle random packed bed”, Suzuki et al., Chemical Engineering Papers Vol. 10 (1984) No. 6, P721-727
“Space ratio of multi-component particle random packed bed with particle size distribution”, Suzuki et al., Chemical Engineering Papers Vol. 11 (1985) No. 4, P438-443

  In the technology disclosed herein, by defining such a high porosity in the inorganic filler layer 20, it is possible to achieve both a high level of safety and long-term durability when the secondary battery is repeatedly used at a high rate. I have to. Thus, the inorganic filler layer 20 with a high porosity prepares the slurry for inorganic filler layer formation which disperse | distributed the inorganic filler and the binder to the appropriate dispersion medium (for example, water), for example, This is made into the negative electrode active material layer 54 It may be formed by supplying to the surface of the separator or the surface on the negative electrode 50 side of the separator 40 and removing the dispersion medium. The binder contained in the inorganic filler layer 20 can be, for example, about 1 to 10% by mass, and is usually about 2% to 5% by mass. At this time, the inorganic filler layer 20 (for example, the first layer 21) having a relatively high porosity can be formed by reducing the amount of the dispersion medium and increasing the solid content concentration. When forming the inorganic filler layer 20 on the surface of the negative electrode active material layer 54, first, the first layer 21 is formed, and then the second layer 22 is formed thereon. When the inorganic filler layer 20 is formed on the surface of the separator 40 on the negative electrode 50 side, the second layer 22 is first formed, and then the first layer 21 is formed thereon. In general, when the porosity of the lower layer (the negative electrode active material layer 54 or the separator 40 and the first layer 21 or the second layer 22) is high, the slurry for forming the inorganic filler layer tends to be absorbed by the lower layer, In order to obtain the first layer 21 or the second layer 22 having a desired porosity, attention should be paid to the amount of the binder, the amount of the dispersion medium, the viscosity of the slurry, and the like.

  The inorganic filler layer 20 disclosed herein may have a two-phase structure including the first layer 21 and the second layer 22, but if the familiarity at the interface between the first layer 21 and the second layer 22 is poor, This is not preferable because the strength of the inorganic filler layer 20 is reduced or partial peeling of the inorganic filler layer 20 is likely to occur. Moreover, it is not preferable that the movement mode of the non-aqueous electrolyte is excessively changed between the first layer 21 and the second layer 22. Therefore, both the first layer 21 and the second layer 22 contain the same two or more inorganic fillers, and the porosity S1 and S2 are adjusted by changing the blending ratio of the two or more inorganic fillers. Is preferred. More specifically, the inorganic filler constituting the inorganic filler layer 20 preferably includes, for example, two or more kinds of fillers having different average major diameters (may be average particle diameters). For example, FIG. 3 is a graph illustrating the relationship between the blending ratio of the mixed filler and the porosity when two types of fillers having different average major diameters are mixed. Thus, the porosity can be easily changed in a wide range by adjusting the mixing ratio of two types of fillers having different average major diameters. Here, by mixing two kinds of granular (substantially spherical) fillers, the porosity can be adjusted while keeping the porosity relatively high, as indicated by white squares in FIG. On the other hand, as shown by a black ▲ in FIG. 3, by mixing a filler with a highly anisotropic shape (for example, a needle shape, a plate shape, a scale shape, a fiber shape, etc.) and a granular filler. The porosity can be adjusted in a wider range from a high range to a low range. Therefore, the inorganic filler layer 20 preferably includes the first layer 21 and the second layer 22 in common with two or more kinds of fillers having different average major axes.

  In the secondary battery for charging / discharging at a high rate, the charge carrier occlusion rate in the negative electrode 50 should be high. For this purpose, for example, it is preferable that a charge carrier, and thus a non-aqueous electrolyte is stably secured in the vicinity of the negative electrode 50 during charging. In other words, for example, when charging / discharging the secondary battery at a high rate, even if a situation occurs in which the nonaqueous electrolyte is moved between the positive electrode 30 and the negative electrode 50, the nonaqueous electrolyte is inorganic during charging. It is preferable that the filler layer 20 can move smoothly toward the negative electrode 50. At this time, it is preferable that the inorganic filler layer 20 (the first layer 21 and the second layer 22, particularly the second layer 22) has a configuration with little resistance to the movement of the nonaqueous electrolytic solution. As a suitable example, the inorganic filler layer 20 preferably has a high penetration rate of the non-aqueous electrolyte. Such an inorganic filler layer 20 can be realized by setting the porosity S1, S2 higher than the conventional one as described above, but suitably adjusting the shape of the inorganic filler constituting the inorganic filler layer 20. However, it can be realized preferably.

  The inorganic filler constituting the inorganic filler layer 20 is generally a powder having an outer shape that is granular (substantially spherical), and its aspect ratio is generally 1 to 1.4 (typically, irrespective of the average particle diameter). It is often in the range of 1 to 1.2). When two kinds of inorganic fillers having a small average aspect ratio are prepared and mixed, for example, the inorganic filler layer 20 simply becomes densely packed and the non-aqueous electrolyte moves easily. There is a high possibility of being disturbed. On the other hand, when an inorganic filler having a relatively large average aspect ratio (for example, needle shape, plate shape, scale shape, fiber shape, etc.) is mixed with an inorganic filler having a small average aspect ratio, the inorganic filler in the inorganic filler layer 20 is mixed. However, it is possible to realize a configuration in which the movement and permeation of the non-aqueous electrolyte are not hindered.

  From such a viewpoint, the inorganic filler constituting the inorganic filler layer 20 preferably includes, for example, two or more kinds of fillers having different average aspect ratios. As a preferred example, the inorganic filler layer 20 preferably includes at least a first filler and a second filler having different average aspect ratios as the inorganic filler constituting the inorganic filler layer. At this time, the average aspect ratio of the first filler is preferably about 1.2 times or more (exceeding 1.2) of the average aspect ratio of the second filler, more preferably about 1.5 times or more, and about twice or more. Is particularly preferable, and may be, for example, approximately 2.5 times or more. The upper limit of the ratio (difference) of the average aspect ratio is not strictly defined because it varies depending on the shape of the first filler having a relatively large average aspect ratio. For example, when the first filler is plate-shaped, for example, the major axis is preferably smaller than the thickness of the first layer 21 and the second layer 22.

  The thickness (average thickness; the same applies hereinafter) of the first layer 21 and the second layer 22 is not strictly limited. When the thickness of the first layer 21 is t1, and the thickness of the second layer 22 is t2, for example, the thickness t1 and t2 may be independently 1 μm or more, for example, 2 μm or more, preferably 3 μm or more. Is more preferable. The thicknesses t1 and t2 may be 10 μm or less independently, for example, preferably 8 μm or less, and more preferably 5 μm or less. The thicknesses t1 and t2 may be about t2 × 0.5 ≦ t1 ≦ t2 × 2, and preferably about t2 × 0.8 ≦ t1 ≦ t2 × 1.2. As an example, t1 = t2 or t1> t2.

  In the invention disclosed herein, the inorganic filler layer 20 may be formed independently and disposed between the negative electrode 50 and the separator 40, or one of the surfaces of the negative electrode 50 and the separator 40. May be formed integrally (in other words, directly). A preferred form is, for example, a configuration in which the inorganic filler layer 20 is directly formed on the surface of the negative electrode 50. In general, when the inorganic filler layer 20 is formed on the surface of the negative electrode 50, the binder contained in the inorganic filler layer 20 covers the surface of the active material particles on the surface of the negative electrode 50, thereby hindering the occlusion and release of charge carriers. It is not preferable. However, the inorganic filler layer 20 disclosed herein has a sufficiently high porosity S1 of the first layer 21 disposed on the negative electrode 50 side, and the binder is suppressed from preventing occlusion and release of charge carriers. Accordingly, the inorganic filler layer 20 having the configuration disclosed herein may be preferably formed on the surface of the negative electrode 50.

As the non-aqueous electrolyte, typically, a supporting salt as an electrolyte (for example, lithium salt, sodium salt, magnesium salt, etc., or lithium salt in a lithium ion secondary battery) is dissolved or dispersed in a non-aqueous solvent. What was made can be used without a restriction | limiting in particular. Or what is called a polymer electrolyte, a solid electrolyte, etc. which the polymer was added to the liquid nonaqueous electrolyte and became gelatinous may be sufficient. As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones that are used as electrolytes in general non-aqueous electrolyte secondary batteries are used without particular limitation. be able to. Specific examples include chain carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), and cyclic carbonates such as propylene carbonate (PC). Such a non-aqueous solvent may be fluorinated. Moreover, a nonaqueous solvent can be used individually by 1 type or in mixture of 2 or more types. As the supporting salt, various types used for general non-aqueous electrolyte secondary batteries can be appropriately selected and employed. For example, the use of lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO ₃ is exemplified. Such supporting salts may be used singly or in combination of two or more. Such a supporting salt is preferably prepared so that the concentration in the non-aqueous electrolyte is within the range of 0.7 mol / L to 1.3 mol / L.

In addition, the nonaqueous electrolyte may contain various additives and the like as long as the characteristics of the nonaqueous electrolyte secondary battery of the present invention are not impaired. As such an additive, a gas generating agent, a film forming agent, etc. can be used for one or more purposes among improvement of input / output characteristics of a battery, improvement of cycle characteristics, improvement of initial charge / discharge efficiency, and the like. Specific examples of such additives include fluorophosphate (preferably difluorophosphate. For example, lithium difluorophosphate represented by LiPO ₂ F ₂ ), lithium bis (oxalato) borate (LiBOB), and the like. An oxalato complex compound is mentioned. The concentration of these additives relative to the entire nonaqueous electrolyte is usually 0.1 mol / L or less (typically 0.005 mol / L to 0.1 mol / L).

  In addition, the non-aqueous electrolyte secondary battery 10 shown in FIG. 1 uses a laminate bag formed as a bag by bonding a metal sheet (typically an aluminum sheet) and a resin sheet as a battery case. However, the battery case of the nonaqueous electrolyte secondary battery 10 is not limited to a laminate bag. For example, the battery case may be a flat or non-flat rectangular battery case or a cylindrical battery case. For example, the battery case may be formed of aluminum, iron, alloys of these metals, high-strength plastic, or the like. Further, the non-aqueous electrolyte secondary battery 10 shown in FIG. 1 is a single cell in which one positive electrode 30 and one negative electrode 50 are housed in a battery case, but the non-aqueous electrolyte secondary battery disclosed herein is a single cell. The secondary battery 10 is not limited to a single cell. The non-aqueous electrolyte secondary battery 10 is, for example, a so-called flat plate type (also referred to as a single-wafer type) battery in which a plurality of positive electrodes 30 and negative electrodes 50 are respectively insulated and stacked by a separator 40. May be. Alternatively, the nonaqueous electrolyte secondary battery 10 is, for example, a so-called wound type in which a long positive electrode 30 and a negative electrode 50 are stacked and wound in a state of being insulated from each other by two separators 40 ( Also called a single wafer type.) A battery may be used.

  Like the battery case of the conventional nonaqueous electrolyte secondary battery, the battery case has a safety valve for discharging the gas generated inside the battery case to the outside, a liquid injection port for injecting the electrolyte, and the like. It may be provided. Further, typically, a positive electrode terminal and a negative electrode terminal for external connection (not shown) can be disposed in the battery case in a state of being insulated from the battery case. The positive electrode terminal and the negative electrode terminal are electrically connected to the positive electrode 30 and the negative electrode 50, respectively, and are configured to supply power to an external load. In FIG. 1, an ammeter is connected to the outside in order to explain the calorific value measurement in the examples described later, but this ammeter is included in the components of the nonaqueous electrolyte secondary battery 10. Absent.

  The non-aqueous electrolyte secondary battery disclosed herein can be used for various applications. For example, the non-aqueous electrolyte secondary battery may have high charge-discharge characteristics and high safety at a high rate that is superior to conventional products. . In addition, these excellent battery performance and reliability (including safety such as thermal stability during overcharge) can be compatible at a high level. Therefore, taking advantage of such characteristics, it can be preferably used in applications requiring high energy density and high input / output density and applications requiring high reliability. Examples of such applications include drive power supplies mounted on vehicles such as plug-in hybrid vehicles, hybrid vehicles, and electric vehicles. Such secondary batteries can typically be used in the form of an assembled battery in which a plurality are connected in series and / or in parallel.

Hereinafter, the nonaqueous electrolyte secondary battery disclosed here was produced as a specific example. It should be noted that the present invention is not intended to be limited to those shown in the specific examples.
[Properties of inorganic filler]
First, as the inorganic filler used to form the inorganic filler layer, two types of granular (substantially spherical) boehmite particles (fillers 1 and 2) and one type of plate-like boehmite particles (filler 3) were prepared. . The major axis, minor axis, aspect ratio, solid bulk specific gravity and porosity of these fillers 1 to 3 were determined, and the results are shown in Table 1 below.

The major axis (a) and minor axis (b) of the inorganic filler were measured by SEM observation, and the aspect ratio (a / b) was calculated from these values. Moreover, the firm bulk density corresponds to the tap bulk density defined in JIS R1628: 1997, and was measured according to the same rule. The porosity is the porosity of the powder after tapping calculated based on the following formula: porosity (%) = (1−solid bulk density / true density of boehmite) × 100. As the true density of boehmite used in this example, 3.1 g / cm ³ was used.

  As shown in Table 1, the filler 1 and the filler 3 are powders having substantially the same bulk density and porosity when compacted alone, and the powders having substantially the same filling density. On the other hand, for example, the porosity when the filler 2 is compacted alone is as low as 65%, and the filling property of the filler 2 is higher than other fillers. Accordingly, a mixed powder is prepared by combining the fillers 1 and 3 with the filler 2. At this time, the porosity is calculated for the mixed powder obtained by changing the mixing ratio of the fillers 1 and 2 and the fillers 3 and 2 from a mass ratio of 1: 0 to 0: 1 in increments of 0.1. This is shown in FIG. The horizontal axis of FIG. 3 shows the mixing ratio of the filler 2.

  As shown in FIG. 3, it was found that, for example, by appropriately blending two different kinds of fillers, the porosity when the mixed powder is compacted can be reduced, and packing can be performed more densely. Here, since the filler 1 and the filler 2 are both granular, the aspect ratio is similar, but the dimensions are greatly different. For example, the major axis has a difference of 6 times. On the other hand, the filler 2 and the filler 3 have different aspect ratios because of their different external shapes, but the dimensional difference on the long side is about twice, and the dimensions on the short side are substantially the same. And it turned out that the direction of the mixed powder of the fillers 1 and 2 can change the porosity in a wider range lower than the mixed powder of the fillers 3 and 2. In other words, it was confirmed that the two kinds of fillers to be mixed were not in the appearance shape, but the larger the difference between the long sides (in other words, the maximum dimension), the lower the porosity after compaction and the denser filling. In addition, it was confirmed that the filling rate could be changed in various ways not only by pressurization but by natural vibration (tapping) only by changing the composition of two different kinds of fillers.

(First embodiment)
[Production of negative electrode]
As the negative electrode active material, powdered natural graphite having an average particle diameter of 15 μm was used. Then, natural graphite (C), styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener are ion-exchanged at a mass ratio of C: SBR: CMC = 98: 1: 1. The negative electrode paste was prepared by kneading with water. This paste was applied to one side of a 10 μm thick copper foil, dried and pressed to obtain a negative electrode having a negative electrode active material layer having a thickness of about 110 μm.

[Formation of inorganic filler layer]
Next, the first layer and the second layer with the porosity changed as the inorganic filler layer are sequentially laminated on the surface of the negative electrode active material layer of the prepared negative electrode, and the inorganic filler layer of Examples 1 to 10 is attached. A negative electrode was produced. Here, the first layer and the second layer are prepared by dispersing an inorganic filler (F), an acrylic polymer (Ac) as a binder, and carboxymethyl cellulose (CMC) as a thickener in water as a dispersion medium. The kneaded inorganic filler layer paste was applied by a die coater and dried each time. Further, the first layer and the second layer are made of F: Ac: CMC = (99−x): x: 1, 1.5 ≦ x ≦ 3. The mass ratio in the range of 2 was determined while appropriately adjusting the dispersion medium. The thicknesses of the first layer and the second layer were both about 4 μm.

  As shown in Table 2 below, in Examples 1 to 5, the porosity of the first layer was changed between 53.0 and 82.0%, and the porosity of the second layer was 67.6%. Constant. In Examples 6 to 10, the porosity of the first layer was similarly changed between 53.0 and 82.0%, and the porosity of the second layer was constant at 59.0%. Here, the porosity of the first layer and the second layer is obtained by mixing any one or two of the three types of fillers 1, 2, and 3 having different shapes with various combinations and blends. It was adjusted. Moreover, since the porosity of the layer used as the foundation | substrate differs in a 1st layer and a 2nd layer, the paste for 2nd layers will be in the state which penetrate | infiltrates into a foundation | substrate layer more easily than the paste for 1st layers. Therefore, in this embodiment, after conducting a preliminary test and specifying in advance the paste conditions (solid content concentration, viscosity) and drying conditions that achieve the desired values of the porosity of the first layer and the second layer, respectively. Each layer was formed under the conditions.

[Electrolyte penetration time of inorganic filler layer]
Moreover, about the negative electrode with an inorganic filler layer of Examples 1-10, the osmosis | permeation time was measured using the nonaqueous electrolyte solution mentioned later, and the result was shown in following Table 2. The permeation time was determined by observing the surface of the second layer with a CCD camera from the direction along the surface of the negative electrode with the inorganic filler layer (cross-sectional view direction), and applying 5 μL of electrolyte to the surface of the second layer of the negative electrode with the inorganic filler layer. The time required for the entire amount of the electrolytic solution to permeate was measured. For the measurement of the permeation time, a contact angle / surface tension measuring device (FTA1000) manufactured by First Ten Angstroms, Inc., USA was used, and when the electrolyte solution contacted the surface of the second layer, The time until the coincidence with the surface of the layer was examined.

[Production of positive electrode]
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (LNMC) as a positive electrode active material powder, AB as a conductive material, and PVDF as a binder, LNMC: AB: PVDF = 90: 8: 2 A positive electrode paste was prepared by mixing with N-methylpyrrolidone (NMP) at a mass ratio of This paste was applied to one side of an aluminum foil having a thickness of 15 μm, dried and pressed to form a positive electrode active material layer, thereby forming a positive electrode.

[Construction of lithium-ion battery]
The negative electrode with an inorganic filler layer and the positive electrode prepared in Examples 1 to 10 prepared above are cut into two sizes so that the capacities are 20 mAh and 150 mAh, overlapped with a separator, and accommodated in a laminate pack together with an electrolytic solution. As a result, a single laminate cell was produced. In addition, as a separator, the microporous sheet | seat which consists of a polyethylene (PE) single layer whose average thickness is 20 micrometers was used. In addition, as a non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC: EMC: DMC = 3: 3: 4 is supported. of LiPF ₆ as a salt were used as dissolved at a concentration of 1 mol / L. The aluminum foil as the positive electrode current collector and the copper foil as the negative electrode current collector were electrically connected to the external positive electrode terminal and the external negative electrode terminal of the laminate pack via lead wires, respectively. Thereby, lithium ion batteries for evaluation of Examples 1 to 10 having two capacities were obtained.

[Measurement of calorific value by needlestick test]
Using prepared lithium ion batteries 1 to 10 for evaluation having a capacity of 20 mAh, the amount of heat generated when an internal short circuit was generated under the following conditions was examined, and safety was evaluated. That is, the lithium ion batteries 1 to 10 for evaluation were subjected to appropriate initial conditioning treatment and adjusted to a state of 25 ° C. and SOC (State of Charge) 100%. Next, a fine internal short circuit is made by piercing a needle having a radius of 0.5 mm and a curvature of φ0.9 mm at the tip at a speed of 0.1 mm / sec so that the positive electrode and the negative electrode communicate with each other in the thickness direction of the laminate cell. Generated. Then, an ammeter is connected between the positive and negative electrodes as illustrated in FIG. 1, and the time from immediately after the short circuit until the needle is blown by heat generation and the amount of current flowing to the external load during that time are measured. Based on this, the calorific value was calculated. The results are shown in Table 2.

[Measurement of resistance change rate]
Using prepared lithium ion batteries 1 to 10 for evaluation having a capacity of 150 mAh, the resistance change rate after repeated charging and discharging was examined, and durability was evaluated. That is, after performing an appropriate initial conditioning treatment on the evaluation lithium ion batteries 1 to 10, impedance measurement was performed at room temperature (25 ° C.), and an initial DC resistance R ₀ was measured. Next, a high-rate pulse charging / discharging is performed for the battery after conditioning at a constant charging rate of 15 seconds at a charging rate of 3.5C and a constant current discharging rate of 20 seconds at a discharging rate of 1.5C. Was subjected to a high rate charge / discharge cycle treatment. Thereafter, impedance measurement was performed again at room temperature (25 ° C.), and DC resistance R ₁ was measured after cycling. From these results, the resistance change rate Rs before and after the high rate cycle was calculated based on the following equation: Rs = R ₁ ÷ R ₀ × 100; The results are shown in Table 2.

[Evaluation]
From the results in Table 1, FIG. 4 shows the relationship between the average porosity of the entire inorganic filler layer and the calorific value, and FIG. 5 shows the relationship between the porosity of the first layer and the calorific value. In FIGS. 4 and 5, for Examples 1 to 5 in which the porosity S2 of the second layer is 67.6%, the marker is a white square “□”, and in Examples 6 to 6 in which the porosity S2 of the second layer is 59.0%. A marker for 10 is indicated by a black diamond “♦”. As can be seen from a comparison between FIG. 4 and FIG. 5, the amount of heat generated during the nail penetration test has a temporary correlation with the average porosity (FIG. 4) of the entire inorganic filler layer, but the porosity S1 of the first layer. It was found that (Figure 5) shows a very good correlation. That is, it was found that the amount of heat generated when a minute short circuit occurred in the lithium ion battery increases as the porosity S1 of the first layer in contact with the negative electrode increases. When the porosity S1 of the first layer exceeds 77.1% (Examples 4 and 9), there is a possibility that the calorific value increases rapidly. For example, 82% (Examples 5 and 10) include an inorganic filler layer. However, it was found that the shrinkage of the separator due to heat generation could not be suppressed, leading to the expansion of the short circuit. Therefore, it can be said that the porosity of the first layer is preferably about 80% or less, and more preferably 77.1% or less for safety. At this time, the porosity S2 of the second layer on the surface side of the inorganic filler layer was 67.6% (Examples 1 to 5) or 59% (Examples 6 to 10), and the calorific value was not affected. From this, it was found that the porosity S2 of the second layer had no effect from the viewpoint of safety at the time of a micro short circuit.

  Next, FIG. 6 shows the relationship between the average porosity of the inorganic filler layer and the electrolyte solution permeation time, and FIG. 7 shows the relationship between the porosity of the first layer and the electrolyte solution permeation time. 6 and FIG. 7, the markers are white squares “□” in Examples 1 to 5 in which the porosity S2 of the second layer is 67.6%, and Examples 6 to 6 in which the porosity S2 of the second layer is 59.0%. A marker for 10 is indicated by a black diamond “♦”. As can be seen from FIGS. 6 and 7, the permeation time of the electrolyte into the inorganic filler layer depends on the average porosity of the entire inorganic filler layer (FIG. 6) and the porosity S1 of the first layer (FIG. 7). The correlation is seen. And it turned out that a big difference is brought about in infiltration time in Examples 1-5 whose porosity S2 of the 2nd layer is 67.6%, and Examples 6-10 of 59%. From this, it was found that the porosity S2 of the second layer should be larger from the viewpoint of the penetration time of the electrolytic solution.

  Here, for example, as shown in FIG. 7, even if the porosity S1 of the first layer is the same, the porosity S2 of the second layer is 59% (Examples 6 to 10) to 67.6% (Example 1). It can be seen that by increasing 8.6% to ~ 5), the penetration time of the electrolytic solution is shortened almost equally to 1.9 to 2.1 seconds. However, when the porosity S1 of the first layer is between 59.1 and 82.0% (Examples 2 to 5, Examples 7 to 10), the penetration time increases at a substantially constant rate as the porosity S1 decreases. On the other hand, it was found that when the porosity S1 decreased to 53.0%, the permeation time increased abruptly. From this, it was found that the porosity S1 of the first layer is preferably higher than 53%, for example 55% or more.

With respect to the resistance change rate due to the high rate cycle, it can be seen from Table 2 that the resistance change tends to decrease as the porosity S1 of the first layer increases, and the resistance change decreases as the porosity S2 of 59% decreases for the second layer. It can be seen that tends to be small. Here, in Examples 1, 2, and 6, it can be seen that the resistance change rate greatly exceeds 110%. These are examples in which the porosity of the second layer is larger than the porosity of the first layer.
The increase in resistance associated with high-rate cycle charging / discharging causes the electrode active material to expand and contract significantly by repeated charging and discharging at a high rate, and return to the electrode body while the electrolyte solution impregnated in the electrode body is discharged. It is thought that this is caused by the gradual progression of electrolyte withering and concentration unevenness in the electrode body. Since the inorganic filler layer does not expand or contract due to high-rate charge / discharge, the first layer adjacent to the surface of the negative electrode active material layer stably retains a large amount of electrolyte solution, while the second layer on the surface side of the inorganic filler layer. If the layer is configured to make it difficult to discharge the electrolytic solution to the outside as much as possible, it is considered that the salt withstanding of the electrolyte can be suppressed, and uneven density and an increase in resistance can be suitably suppressed. In addition, from the viewpoint of the penetration time of the electrolytic solution, it was found that the porosity S2 of the second layer should be large. However, considering the movement of the electrolyte during battery use, that is, the rate of change in resistance due to the high rate cycle, the first layer secures the electrolyte by increasing the porosity S1, and the second layer is compared with the first layer. It can be said that it is effective to make the porosity S2 smaller than the porosity S1 so that the electrolyte is relatively difficult to move.

(Embodiment 2)
In the same manner as in the first embodiment, lithium ion secondary batteries for evaluation of Examples 11 to 17 were manufactured, and the migration resistance of the nonaqueous electrolytic solution in the inorganic filler layer was examined. In Examples 11 to 17, in order to form the first layer and the second layer as the inorganic filler layer, any one of the fillers 1 to 3 is used alone, or two are mixed to form an inorganic filler. . Specifically, as shown in Table 3 below, in Examples 11 to 17, the porosity S1 of the first layer was all set to 59.1%. And in Examples 11-13, the inorganic filler which mixed the substantially granular filler 1 and the filler 2 was used for formation of a 2nd layer, and the porosity S2 of the 2nd layer was changed by 53.0-79.7%. Moreover, in Examples 14-17, the inorganic filler which mixed the substantially granular filler 1 and the plate-shaped filler 3 was used for formation of a 2nd layer, and the porosity S2 of a 2nd layer was 58.0-74.0%. It was changed with.

  And about the prepared negative electrode with an inorganic filler layer, it carried out similarly to said 1st embodiment, and measured "electrolyte solution penetration time of an inorganic filler layer". The results are shown in Table 3 below. For reference, Table 3 also shows the results of Examples 2 and 7 using the granular filler 1 and the filler 2 in the first embodiment. Further, FIG. 8 shows the relationship between the porosity S2 of the second layer and the permeation time of the electrolytic solution.

[Evaluation]
In FIG. 8, in Examples 2, 7, and 11 to 13 where the second layer is formed by the granular fillers 1 and 2, the marker is a black circle “●”, and the second layer is formed by the granular filler 1 and the plate-like filler 3. In Examples 14 to 17, the markers are indicated by white triangles “Δ”.
As is clear from FIG. 8, in Examples 2, 7, and 11 to 13 using only the granular filler, the time required for the penetration of the electrolytic solution tends to increase as the porosity S2 of the second layer decreases. I was able to confirm. In particular, in Examples 11 and 7 in which the porosity S2 is smaller than 60%, it has been found that the permeation time rapidly increases. In FIG. 6 and FIG. 7 of the first embodiment, this is consistent with the fact that the smaller the porosity S2 of the second layer, the longer the permeation time of the electrolytic solution. In addition, although the example in which the porosity S1 of the first layer is smaller than the porosity S2 of the second layer is included in the above example, as shown in FIG. In the present embodiment, the porosity S1 of the first layer is unified at 59.1% because the rate S1 does not greatly affect the permeation time of the electrolytic solution if it exceeds 53%.

On the other hand, in Examples 14 to 17 in which the granular filler 1 and the plate-like filler 3 are mixed and used, the penetration time of the electrolytic solution is as short as about 2 seconds without depending on the porosity S2 of the second layer. It was confirmed that it was shortened. This is considered to be due to the electrolytic solution penetrating linearly in the second layer along the surface of the plate-like filler. In other words, it is considered that the penetration path of the electrolytic solution can be set linearly and at a short distance due to the presence of the plate-like filler. Therefore, it is confirmed that the penetration time of the electrolyte solution (improvement of the penetration rate) can be shortened by using a material with a high aspect ratio such as a plate shape, scale shape, or fiber shape as the inorganic filler constituting the second layer. did it.
As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

10 Secondary battery 20 Inorganic filler layer 21 First layer 22 Second layer 30 Positive electrode 40 Separator 50 Negative electrode

Claims (5)

A positive electrode, a negative electrode,
A separator disposed between the positive electrode and the negative electrode;
An inorganic filler layer disposed between the negative electrode and the separator;
A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte,
The inorganic filler layer is
A first layer disposed on the negative electrode side;
A second layer adjacent to the first layer and disposed on the separator side,
When the porosity of the first layer is represented by S1 and the porosity of the second layer is represented by S2, the relationship between S1 and S2 is as follows:
S1 ≧ S2; and 53 <S1 ≦ 77.1;
Satisfying the non-aqueous electrolyte secondary battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the inorganic filler layer includes two or more kinds of fillers having different average aspect ratios. The inorganic filler layer includes a first filler and a second filler having different average aspect ratios,
The nonaqueous electrolyte secondary battery according to claim 2, wherein an average aspect ratio of the first filler is twice or more an average aspect ratio of the second filler.   4. The non-aqueous electrolyte secondary battery according to claim 1, wherein each of the first layer and the second layer includes two or more types of fillers having different average major axes.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the first layer is formed so as to be directly bonded to the surface of the negative electrode.

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