secondary batteries

Abstract

To provide a secondary battery using positive electrode active material having a Li(Ni-Mn-Co)O2 composition, where adhesion between a positive electrode active material layer and a solid electrolyte layer is improved and increase in interface resistance caused by progress of a charging / discharge cycle is suppressed.SOLUTION: A secondary battery has a power generation element 21 including a positive electrode including a positive electrode active material layer 15 containing positive electrode active material composed of secondary particles, a negative electrode, and a solid electrolyte layer 17 that is interposed between the positive electrode and the negative electrode and contains a solid electrolyte, the positive electrode active material including Li(Ni-Mn-Co)O2 or NMC complex oxide having a composition obtained by replacing one or some of these transition metals with other elements, the average particle size of the secondary particles being equal to or smaller than 15.0 μm, the average particle size of primary particles constituting the secondary particles being equal to or larger than 0.5 μm. At least one of the positive electrode active material layer 15 and the solid electrolyte layer 17 contains solid electrolyte containing halogen; the other contains a binder having a functional group having an unshared electron pair.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a secondary battery. [Background technology]

[0002] In recent years, there has been a strong desire to reduce carbon dioxide emissions in order to combat global warming. The automotive industry is hoping that the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs) will help reduce carbon dioxide emissions, and there has been active development of non-aqueous electrolyte secondary batteries, such as secondary batteries for driving motors, which hold the key to putting these vehicles into practical use.

[0003] Secondary batteries for driving motors are required to have extremely high output characteristics and high energy compared to consumer lithium-ion secondary batteries used in mobile phones, laptops, etc. Therefore, lithium-ion secondary batteries, which have the highest theoretical energy of all practical batteries, have attracted attention and are currently being rapidly developed.

[0004] Currently widely used lithium-ion secondary batteries use flammable organic electrolytes, and these liquid-based lithium-ion secondary batteries require stricter safety measures against leakage, short circuits, overcharging, and other issues than other batteries.

[0005] Therefore, in recent years, there has been active research and development into all-solid-state batteries, such as all-solid-state lithium secondary batteries that use oxide- or sulfide-based solid electrolytes. Solid electrolytes are materials primarily composed of ionic conductors that allow ionic conduction in a solid state. Therefore, all-solid-state lithium secondary batteries, in principle, do not encounter the various problems associated with flammable organic electrolytes that occur in conventional liquid-based lithium-ion secondary batteries. Furthermore, the use of high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials generally leads to significant improvements in the output density and energy density of batteries.

[0006] Lithium-metal composite oxides and the like are sometimes used as positive electrode active materials for lithium-ion secondary batteries, and powders of these composite oxides may be composed of primary particles and secondary particles formed by aggregation of the primary particles. It has been proposed that powdered lithium composite oxides of monodispersed primary particles (single particles) containing lithium and one element selected from the group consisting of cobalt, nickel, and manganese as the main components have the advantage of having no grain boundaries and being less susceptible to cracking or breakage during molding of the positive electrode material.

[0007] Incidentally, Patent Document 1 aims to reduce the interfacial resistance between solid particles in an all-solid-state lithium secondary battery using a positive electrode active material such as a lithium metal composite oxide by modifying the binder contained in the electrode active material layer or the solid electrolyte layer. Specifically, Patent Document 1 claims that by including a predetermined inorganic solid electrolyte and cellulose polymer in either the electrode active material layer or the solid electrolyte layer, it is possible to reduce the interfacial resistance between solid particles and achieve high ionic conductivity. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-191864 Summary of the Invention [Problem to be solved by the invention]

[0009] According to the investigations of the present inventors, it has been found that there is still room for improvement in the technology disclosed in Patent Document 1. In particular, it has been found that when a single-crystal NMC composite oxide having a composition in which Li(Ni-Mn-Co)O2 or a portion of these transition metals is substituted with other elements is used as a positive electrode active material, the adhesion between the positive electrode active material layer and the solid electrolyte layer decreases, and the interfacial resistance between them increases as the charge-discharge cycle progresses.

[0010] Therefore, the present invention aims to provide a means for improving the adhesion between the positive electrode active material layer and the solid electrolyte layer in a secondary battery that uses, as the positive electrode active material, Li(Ni-Mn-Co)O2 or a single-crystal NMC composite oxide having a composition in which part of these transition metals is substituted with other elements, and capable of suppressing an increase in interface resistance with the progress of charge-discharge cycles. [Means for solving the problem]

[0011] The present inventors have conducted extensive research in light of the above-mentioned problems, and as a result have found that in a secondary battery using, as a positive electrode active material, a single-crystal NMC composite oxide having a composition in which Li(Ni-Mn-Co)O or a transition metal thereof is partially substituted with another element, the above-mentioned problems can be solved by incorporating a solid electrolyte containing a halogen element into at least one of the positive electrode active material layer and the solid electrolyte layer, and incorporating a binder having a functional group with an unshared electron pair into the other layer, thereby completing the present invention.

[0012] According to one aspect of the present invention, there is provided a secondary battery having a power generating element including a positive electrode including a positive electrode active material layer containing a positive electrode active material composed of secondary particles, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte. The positive electrode active material includes Li(Ni-Mn-Co)O or an NMC composite oxide having a composition in which some of the transition metals in these are substituted with other elements. The average particle size of the secondary particles is 15.0 μm or less, and the average particle size of the primary particles constituting the secondary particles is 0.5 μm or more. The battery is characterized in that at least one of the positive electrode active material layer and the solid electrolyte layer contains a solid electrolyte containing a halogen element, and the other contains a binder having a functional group with an unshared electron pair. [Effects of the Invention]

[0013] According to the present invention, in a secondary battery using, as a positive electrode active material, a single-crystal NMC composite oxide having a composition in which Li(Ni-Mn-Co)O2 or a portion of these transition metals is substituted with other elements, the adhesion between the positive electrode active material layer and the solid electrolyte layer can be improved, and an increase in interface resistance with the progress of charge-discharge cycles can be suppressed. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view showing the appearance of a flat laminated type all-solid-state lithium ion secondary battery, which is one embodiment of the lithium ion secondary battery according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line 2-2 shown in FIG. [Figure 3] FIG. 3 is a perspective view of a stacked battery according to one embodiment of the present invention. [Figure 4] FIG. 4 is a side view seen from the direction A shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] 《Secondary battery》 One embodiment of the present invention is a secondary battery having a power generating element including: a positive electrode including a positive electrode active material layer containing a positive electrode active material formed of secondary particles; a negative electrode; and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte, wherein the positive electrode active material includes Li(Ni-Mn-Co)O or an NMC composite oxide having a composition in which a portion of the transition metal in Li(Ni-Mn-Co)O is substituted with another element; the average particle size of the secondary particles is 15.0 μm or less; and the average particle size of primary particles constituting the secondary particles is 0.5 μm or more; and at least one of the positive electrode active material layer and the solid electrolyte layer contains a solid electrolyte containing a halogen element, and the other contains a binder having a functional group with an unshared electron pair.

[0016] Hereinafter, embodiments of the secondary battery according to the present invention will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the claims and is not limited to the following embodiments. Note that the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0017] FIG. 1 is a perspective view showing the appearance of a flat-layered all-solid-state lithium secondary battery, which is one embodiment of the secondary battery according to the present invention. FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1. The layered structure allows the battery to be compact and have a high capacity. In this specification, the flat-layered non-bipolar lithium ion secondary battery shown in FIGS. 1 and 2 (hereinafter also simply referred to as a "layered battery") will be described in detail as an example. However, in terms of the internal electrical connection configuration (electrode structure) of the lithium ion secondary battery according to this embodiment, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries.

[0018] 1, the stacked battery 10a has a flat, rectangular shape, with a negative electrode current collector 25 and a positive electrode current collector 27 extending from both sides for extracting power. The power generating element 21 is wrapped in the battery exterior material (laminate film 29) of the stacked battery 10a, and the periphery is heat-sealed, with the negative electrode current collector 25 and positive electrode current collector 27 extending to the outside.

[0019] The lithium ion secondary battery according to this embodiment is not limited to a laminated, flat shape. A wound lithium ion secondary battery may be cylindrical, or may be a cylindrical battery modified into a rectangular, flat shape, and is not particularly limited. The cylindrical battery may use a laminate film or a conventional cylindrical can (metal can) as its exterior material, and is not particularly limited. Preferably, the power generating element is housed inside a laminate film containing aluminum. This configuration can achieve weight reduction.

[0020] Furthermore, there are no particular limitations on how the current collector plates (25, 27) shown in Fig. 1 are taken out. The negative current collector plate 25 and the positive current collector plate 27 may be taken out from the same side, or the negative current collector plate 25 and the positive current collector plate 27 may each be divided into multiple pieces and taken out from each side, and so on, and are not limited to what is shown in Fig. 1. Furthermore, in a wound-type lithium-ion battery, terminals may be formed using, for example, a cylindrical can (metal can) instead of tabs.

[0021] 2, the stacked battery 10a of this embodiment has a structure in which a flat, generally rectangular power generating element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior material. Here, the power generating element 21 has a configuration in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are stacked. The positive electrode has a structure in which positive electrode active material layers 15 containing a positive electrode active material are disposed on both sides of a positive electrode current collector 11". The negative electrode has a structure in which negative electrode active material layers 13 containing a negative electrode active material are disposed on both sides of a negative electrode current collector 11'. Specifically, the positive electrode, solid electrolyte layer, and negative electrode are stacked in this order such that one positive electrode active material layer 15 faces an adjacent negative electrode active material layer 13 with a solid electrolyte layer 17 interposed therebetween. As a result, the adjacent positive electrode, solid electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, the stacked battery 10a shown in FIG. 1 can also be said to have a structure in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel. Furthermore, a constraining pressure is applied to the stacked battery 10a in the stacking direction of the power generating element 21 by a pressure member (not shown). Therefore, the volume of the power generating element 21 is kept constant.

[0022] As shown in FIG. 2, the outermost positive electrode current collectors located on both outermost layers of the power generating element 21 each have a positive electrode active material layer 15 disposed on only one side, but active material layers may be provided on both sides. That is, instead of using a current collector exclusively for the outermost layer with an active material layer provided on only one side, a current collector having active material layers on both sides may be used as the outermost current collector. In some cases, the negative electrode active material layer 13 and the positive electrode active material layer 15 may be used as the negative electrode and the positive electrode, respectively, without using the current collectors (11', 11")

[0023] Negative electrode current collector 11′ and positive electrode current collector 11″ are respectively attached with negative electrode current collector (tab) 25 and positive electrode current collector (tab) 27 that are electrically connected to the respective electrodes (positive and negative electrodes), and are structured so as to be sandwiched between the ends of laminate film 29, which is the battery outer casing material, and extended to the outside of laminate film 29. Positive electrode current collector 27 and negative electrode current collector 25 may be attached to positive electrode current collector 11″ and negative electrode current collector 11′ of the respective electrodes by ultrasonic welding, resistance welding, or the like, via positive electrode leads and negative electrode leads (not shown) as necessary.

[0024] Fig. 3 is a perspective view of a stacked battery according to one embodiment of the present invention, and Fig. 4 is a side view seen from direction A shown in Fig. 3.

[0025] As shown in FIGS. 3 and 4 , the stacked battery 100 according to this embodiment includes a power generating element 21 sealed in a laminate film 29 as shown in FIGS. 1 and 2 , two metal plates 200 sandwiching the power generating element 21 sealed in the laminate film 29, and bolts 300 and nuts 400 as fastening members. The fastening members (bolts 300 and nuts 400) function to secure the power generating element 21 sealed in the laminate film 29 in a sandwiched state between the metal plates 200. As a result, the metal plates 200 and the fastening members (bolts 300 and nuts 400) function as pressure members that pressurize (restrain) the power generating element 21 in the stacking direction. Note that the pressure members are not particularly limited as long as they are members that can pressurize the power generating element 21 in the stacking direction. A combination of a plate made of a rigid material, such as the metal plate 200, and the above-described fastening members is typically used as the pressure member. Furthermore, the fastening members are not limited to the bolts 300 and nuts 400, and may include tension plates or the like that fix the ends of the metal plates 200 so as to restrain the power generating element 21 in the stacking direction.

[0026] The lower limit of the load applied to the power generating element 21 (restraint pressure in the stacking direction of the power generating element) is, for example, 0.1 MPa or more, preferably 1 MPa or more, more preferably 3 MPa or more, and even more preferably 5 MPa or more. The upper limit of the restraint pressure in the stacking direction of the power generating element is, for example, 100 MPa or less, preferably 70 MPa or less, more preferably 40 MPa or less, and even more preferably 10 MPa or less.

[0027] The main components of the secondary battery according to this embodiment will be described below.

[0028] [Current collector] The current collector has a function of mediating the transfer of electrons from the electrode active material layer. There are no particular limitations on the material constituting the current collector. For example, metals and conductive resins can be used as the material constituting the current collector.

[0029] Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. Other examples include clad materials of nickel and aluminum, and clad materials of copper and aluminum. Furthermore, foils in which aluminum is coated on a metal surface may also be used. Among these, aluminum, stainless steel, copper, and nickel are preferred from the viewpoints of electronic conductivity, battery operating potential, and adhesion of the negative electrode active material to the current collector by sputtering.

[0030] The latter conductive resin may be a resin obtained by adding a conductive filler to a non-conductive polymer material as required.

[0031] The current collector may have a single layer structure made of a single material, or may have a laminate structure made of an appropriate combination of layers made of these materials. From the viewpoint of reducing the weight of the current collector, it is preferable that the current collector includes at least a conductive resin layer made of a resin having electrical conductivity. Furthermore, from the viewpoint of blocking the movement of lithium ions between the cell layers, a metal layer may be provided on a part of the current collector. Furthermore, if the negative electrode active material layer and the positive electrode active material layer described later are electrically conductive and can perform a current collecting function, it is not necessary to use a current collector as a separate member from these electrode active material layers. In such a configuration, the negative electrode active material layer described later constitutes the negative electrode, and the positive electrode active material layer described later constitutes the positive electrode.

[0032] [Cathode active material layer] In the secondary battery according to this embodiment, the positive electrode active material layer contains a positive electrode active material. Here, the positive electrode active material essentially contains Li(Ni-Mn-Co)O2 or a lithium transition metal composite oxide (hereinafter also simply referred to as "NMC composite oxide") having a composition in which a portion of the transition metal is substituted with another element. The NMC composite oxide has a layered crystal structure in which lithium atomic layers and transition metal (Mn, Ni, and Co) atomic layers are stacked alternately with oxygen atomic layers interposed therebetween. One Li atom is contained per atom of the transition metal M, and the amount of Li that can be extracted is twice that of spinel-type lithium manganese oxide, i.e., the supply capacity is doubled, resulting in high capacity.

[0033] As described above, the NMC composite oxide also includes composite oxides in which a portion of the transition metal element is replaced with another metal element, such as Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu, Ag, or Zn, preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, or Cr, more preferably Ti, Zr, P, Al, Mg, or Cr, and even more preferably Ti, Zr, Al, Mg, or Cr from the viewpoint of improving cycle characteristics.

[0034] Since the NMC composite oxide has a high theoretical discharge capacity, it is preferable to use the NMC composite oxide represented by the general formula (1): Li a Ni b Mn c Co d M xO2 (wherein, in the formula, a, b, c, d, and x satisfy 0.98 ≤ a ≤ 1.2, 0.6 ≤ b ≤ 0.9, 0 < c ≤ 0.4, 0 < d ≤ 0.4, 0 ≤ x ≤ 0.3, and b + c + d + x = 1. M is at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, 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. From the perspective of a high theoretical discharge capacity, it is preferably 0.6 ≤ b ≤ 0.9 as described above. However, from the perspective of improving the adhesion between the positive electrode active material layer and the solid electrolyte layer and suppressing an increase in the interfacial resistance between them, it is more preferably that b satisfies 0.6 ≤ b ≤ 0.8, and even more preferably that b satisfies 0.6 ≤ b ≤ 0.7.

[0035] In the secondary battery according to this embodiment, the cathode active material contained in the cathode active material layer is composed of secondary particles. Here, "secondary particles" refers to aggregates formed by aggregation of primary particles (single particles). The secondary battery according to this embodiment is characterized in that the average particle diameter (arithmetic mean diameter) of the secondary particles constituting the cathode active material is controlled to 15.0 μm or less, and the average particle diameter (arithmetic mean diameter) of the primary particles constituting the secondary particles is controlled to 0.5 μm or more. In this specification, a cathode active material having such an average particle diameter profile is referred to as "single crystal type." In this specification, "particle diameter" refers to the maximum distance between any two points on the observed particle outline. The average particle diameters of the active material and the solid electrolyte are measured by the methods described in the Examples section below. The average particle diameter of the secondary particles constituting the cathode active material is preferably 12.0 μm or less, more preferably 10.0 μm or less, and even more preferably 7.0 μm or less. There is no particular lower limit to the average particle size of the secondary particles, but it is usually 5.0 μm or more, and from the viewpoint of effectively obtaining the effects of the present invention, it is preferably 6.0 μm or more. Furthermore, the average particle size of the primary particles that make up the secondary particles is preferably 1.0 μm or more, and more preferably 2.0 μm or more. There is no particular upper limit to the average particle size of the secondary particles, but it is usually 5.5 μm or less, and from the viewpoint of effectively obtaining the effects of the present invention, it is preferably 5.0 μm or less.

[0036] The proportion of particles consisting of a single crystallite among the primary particles constituting the secondary particles is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more. This is preferable because it makes it easier to obtain a positive electrode active material having the specified particle size profile of the present invention.

[0037] There are no particular limitations on the method for controlling the average particle size of the positive electrode active material particles to the above-mentioned configuration, and conventionally known knowledge that can control the average particle size of the positive electrode active material particles can be appropriately referenced. Specifically, for example, reference can be made to the methods disclosed in patent documents such as Japanese Patent No. 6574222 and Japanese Patent No. 5702289, and non-patent documents such as Solid State Ionics, Volume 345, February 2020, 115200, and Journal of the Electrochemical Society, 165(5)A1038-A1045(2018).

[0038] The positive electrode active material layer may contain a positive electrode active material other than the above-mentioned positive electrode active materials. Examples of such positive electrode active materials include layered rock salt active materials such as LiCoO2, LiMnO2, LiNiO2, and LiVO2; LiMn2O4; LiNi 0.5 Mn 1.5 Spinel-type active materials such as O4, olivine-type active materials such as LiFePO4 and LiMnPO4, Si-containing active materials such as Li2FeSiO4 and Li2MnSiO4, and Li4Ti5O 12 However, the content of the NMC composite oxide relative to the total amount (100% by mass) of the positive electrode active material contained in the positive electrode active material layer is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% 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.

[0039] The positive electrode active material layer further includes a solid electrolyte. By including the solid electrolyte in the positive electrode active material layer, the ionic conductivity of the positive electrode active material layer can be improved. Examples of the solid electrolyte include sulfide solid electrolytes and oxide solid electrolytes. However, from the viewpoint of excellent ionic conductivity and further improvement of battery performance, a sulfide solid electrolyte is preferred.

[0040] Examples of sulfide solid electrolytes include LiI-Li2S-SiS2, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, LiI-Li3PS4, LiI-LiBr-Li3PS4, Li3PS4, Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z m S n (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In). The term "LiS-P2S5" refers to a sulfide solid electrolyte obtained using a raw material composition containing LiS and P2S5, and the same applies to other terms.

[0041] The sulfide solid electrolyte may have, for example, a Li3PS4 skeleton, a Li4P2S7 skeleton, or a Li4P2S6 skeleton. Examples of sulfide solid electrolytes having a Li3PS4 skeleton include LiI-Li3PS4, LiI-LiBr-Li3PS4, and Li3PS4. Examples of sulfide solid electrolytes having a Li4P2S7 skeleton include Li-PS-based solid electrolytes known as LPS (for example, Li7P3S 11 ) can be mentioned. In addition, examples of sulfide solid electrolytes include Li (4-x) Ge (1-x) P xAn LGPS or the like represented by S4 (where 0 < x < 1) may be used. Among them, the sulfide solid electrolyte is preferably a sulfide solid electrolyte containing P element, and more preferably a material mainly composed of Li2S-P2S5. Further, examples of the sulfide solid electrolyte containing halogen include argyrodite-type solid electrolyte (Li6PS5X (X is Cl, Br or I)), which is also a material that can be preferably used.

[0042] Also, the sulfide solid electrolyte may be a sulfide glass, a crystallized sulfide glass, or a crystalline material obtained by a solid-phase method. The sulfide glass can be obtained, for example, by performing mechanical milling (such as a ball mill) on a raw material composition. Also, the crystallized sulfide glass can be obtained, for example, by heat-treating the sulfide glass at a temperature above the crystallization temperature. The ionic conductivity (for example, Li ion conductivity) of the sulfide solid electrolyte at room temperature (25 °C) is, for example, -5 preferably 1×10 -4 S / cm or more, and more preferably 1×10

[0043] Examples of the oxide solid electrolyte include compounds having a NASICON-type structure. An example of a compound having a NASICON-type structure is a compound represented by the general formula Li 1+x Al x Ge 2-x (PO4)3 (0 ≦ x ≦ 2) (LAGP), a compound represented by the general formula Li 1+x Al x Ti 2-x (PO4)3 (0 ≦ x ≦ 2) (LATP), etc. Further, as other examples of the oxide solid electrolyte, LiLaTiO (for example, Li 0.34 La 0.51 TiO3), LiPON (for example, Li 2.9 ) PO 3.3 N 0.46 ), LiLaZrO (for example, Li7La3Zr2O12 ) etc.

[0044] The positive electrode active material layer may further contain at least one of a conductive additive and a binder in addition to the above-mentioned positive electrode active material and solid electrolyte. There are no particular restrictions on the amount of each component contained in the positive electrode active material layer, but the amount of the solid electrolyte is preferably 15 to 40 mass%, the amount of the conductive additive is preferably 10 to 30 mass%, and the amount of the binder is preferably 1 to 5 mass%, relative to 100 mass% of the total amount of the positive electrode active material layer.

[0045] The thickness of the positive electrode active material layer varies depending on the intended configuration of the all-solid-state battery, but is preferably within the range of, for example, 0.1 to 1000 μm.

[0046] [Solid electrolyte layer] In the secondary battery according to this embodiment, the solid electrolyte layer is interposed between the above-described positive electrode active material layer and negative electrode active material layer and is a layer essentially containing a solid electrolyte. Specific forms of the solid electrolyte contained in the solid electrolyte layer may be the same as those exemplified and preferred forms described in the section on the positive electrode active material layer. That is, the solid electrolyte layer preferably contains a sulfide solid electrolyte. The solid electrolyte layer may further contain a binder in addition to the above-described solid electrolyte. There are no particular restrictions on the amount of each component contained in the solid electrolyte layer, but the amount of the binder is preferably 2 to 8 mass % relative to 100 mass % of the total amount of the solid electrolyte layer.

[0047] The thickness of the solid electrolyte layer varies depending on the configuration of the intended lithium ion secondary battery, but from the viewpoint of improving the volumetric energy density of the battery, it is preferably 600 μm or less, more preferably 500 μm or less, and even more preferably 400 μm or less. On the other hand, there is no particular restriction on the lower limit of the thickness of the solid electrolyte layer, but it is preferably 10 μm or more, more preferably 50 μm or more, and even more preferably 100 μm or more.

[0048] One feature of the secondary battery according to this embodiment is that at least one of the cathode active material layer 15 and the solid electrolyte layer 17 contains a solid electrolyte containing a halogen element, and the other contains a binder having a functional group with an unshared electron pair. By virtue of this feature, the secondary battery according to this embodiment, in a secondary battery using the predetermined single-crystal NMC composite oxide as the cathode active material, exhibits the effect of improving adhesion between the cathode active material layer and the solid electrolyte layer and suppressing an increase in interfacial resistance with the progress of charge-discharge cycles. The mechanism by which this effect is achieved by the configuration of this embodiment is not fully understood, but the following mechanism is presumed. Specifically, in a secondary battery using the predetermined single-crystal NMC composite oxide as the cathode active material, the surfaces of the cathode active material particles are smooth, making it difficult for an anchor effect to occur between the cathode active material contained in the cathode active material layer and the solid electrolyte layer. As a result, the adhesion between the positive electrode active material layer and the solid electrolyte layer is insufficient to begin with, and furthermore, due to the expansion and contraction of the positive electrode active material as charge and discharge proceed, the adhesion between these layers gradually decreases, resulting in an increase in interfacial resistance. In contrast, in the secondary battery according to the present embodiment, a halogen bond is formed between the unshared electron pair of the functional group having an unshared electron pair possessed by the binder according to the present embodiment, which is contained in one of the positive electrode active material layer and the solid electrolyte layer, and the halogen element of the halogen-containing solid electrolyte contained in the other. Note that a "halogen bond" is a type of non-covalent interaction that acts between a halogen atom acting as a Lewis acid and a Lewis base, and the halogen atom functions as an electrophilic species in the formation of the halogen bond. The formation of many such halogen bonds is thought to improve the adhesion between the positive electrode active material layer and the solid electrolyte layer, thereby preventing an increase in interfacial resistance as charge and discharge proceed.

[0049] As described above, in the secondary battery according to this embodiment, at least one of the positive electrode active material layer 15 and the solid electrolyte layer 17 may contain a solid electrolyte containing a halogen element, and the other may contain a binder having a functional group having an unshared electron pair. Examples of such a configuration include a configuration in which the positive electrode active material layer 15 contains a solid electrolyte containing a halogen element, and the solid electrolyte layer 17 contains a binder having a functional group having an unshared electron pair; a configuration in which the positive electrode active material layer 15 contains a solid electrolyte containing a halogen element and a binder having a functional group having an unshared electron pair, and the solid electrolyte layer 17 contains a binder having a functional group having an unshared electron pair; a configuration in which the positive electrode active material layer 15 contains a binder having a solid electrolyte containing a halogen element, and the solid electrolyte layer 17 contains a solid electrolyte containing a halogen element and a binder having a functional group having an unshared electron pair; The positive electrode active material layer 15 may contain a binder having a functional group with an unshared electron pair, and the solid electrolyte layer 17 may contain a solid electrolyte containing a halogen element; the positive electrode active material layer 15 may contain a solid electrolyte containing a halogen element and a binder having a functional group with an unshared electron pair, and the solid electrolyte layer 17 may contain a solid electrolyte containing a halogen element; the positive electrode active material layer 15 may contain a solid electrolyte containing a halogen element, and the solid electrolyte layer 17 may contain a solid electrolyte containing a halogen element and a binder having a functional group with an unshared electron pair; or both the positive electrode active material layer 15 and the solid electrolyte layer 17 may contain a solid electrolyte containing a halogen element and a binder having a functional group with an unshared electron pair. Among these, it is preferable that the positive electrode active material layer 15 contains a solid electrolyte containing a halogen element, and the solid electrolyte layer 17 contains a binder having a functional group with an unshared electron pair. With this configuration, the unshared electron pair derived from the binder contained in the solid electrolyte layer and the lithium ions (Li +) generates an ion-dipole interaction, which, together with the formation of the halogen bond described above, further improves the adhesion between these layers and the effect of preventing interfacial resistance. Furthermore, it is particularly preferable that both the positive electrode active material layer 15 and the solid electrolyte layer 17 contain a solid electrolyte containing a halogen element and a binder having a functional group with an unshared electron pair. This configuration further improves the adhesion between the positive electrode active material layer 15 and the solid electrolyte layer 17, which can be particularly effective in reducing interfacial resistance.

[0050] The specific configuration of the "halogen-containing solid electrolyte" is not particularly limited, and a wide variety of conventionally known solid electrolytes having ion conductivity containing a halogen element can be used. Among these, a halogen-containing solid electrolyte that is excellent in ion conductivity and electrochemical stability (durability) is preferably a halogen-containing sulfide solid electrolyte. A preferred example of such a halogen-containing sulfide solid electrolyte is the argyrodite-type solid electrolyte (Li6PS5X (X is Cl, Br, or I)). Furthermore, halogen-containing sulfide solid electrolytes described in prior art documents such as JP 2017-183210 A, JP 2018-49834 A, and JP 2020-115425 A can also be suitably used in the secondary battery according to the present embodiment.

[0051] Next, a "binder having a functional group having an unshared electron pair" (hereinafter also simply referred to as "the binder according to the present embodiment") will be described. First, an "unshared electron pair" is also called a "lone pair" or a "non-bonding electron pair," and refers to an electron pair that is a pair of two outer shell electrons of an atom that is not involved in a bond with another atom. Examples of such functional groups having an unshared electron pair include one or more selected from the group consisting of an amide group, a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a methylenedioxy group, a phenoxy group, a carboxy group, a methoxycarbonyl group, an ethoxycarbonyl group, an acetoxy group, a benzoyloxy group, an acetyl group, a propionyl group, an acryloyl group, a methacryloyl group, a malonyl group, a benzoyl group, a hydroxy group, a hydroperoxy group, an alkyleneoxy group, an epoxy group, a dioxy group, a carbonyl group, a mercapto group, a thio group, a sulfo group, a sulfinyl group, a sulfonyl group, a sulfoamino group, a nitro group, a cyano group, an isocyano group, a nitroso group, an imidazole group, an amino group, a ureido group, a methylamino group, an imino group, a diazo group, an azo group, an azide group, and a diazoamino group. All of these functional groups have unshared electron pairs and are suitable for forming the above-mentioned halogen bonds.

[0052] The binder according to this embodiment functions as a binder (binding agent). Therefore, when the binder is contained in the positive electrode active material layer 15 or the solid electrolyte layer 17, the binder functions to bind other components contained in each layer together. Because of this function, the binder according to this embodiment usually contains a polymer (is in the form of a polymer). There are no particular limitations on the specific form of the polymer, and it may be any polymer having a functional group with the above-mentioned unshared electron pair. For example, a vinyl (co)polymer obtained by (co)polymerizing a vinyl monomer is a suitable example.

[0053] The binder according to the present embodiment preferably contains a polymer having two or more types of functional groups having unshared electron pairs. This configuration has the advantage of improving the adhesion between layers more effectively than when only one type of functional group is used. For example, when the polymer constituting the binder according to the present embodiment is an acrylic polymer having an acryloyl group or a methacryloyl group as the functional group having an unshared electron pair, the polymer preferably has a functional group having an unshared electron pair other than an acryloyl group or a methacryloyl group. In this embodiment, as the functional group having an unshared electron pair other than an acryloyl group or a methacryloyl group, an amide group, a carboxy group, a hydroxy group, a hydroperoxy group, an alkyleneoxy group, an epoxy group, a carbonyl group, a mercapto group, a thio group, a sulfo group, a sulfinyl group, a sulfonyl group, a sulfoamino group, a nitro group, a cyano group, an isocyano group, an amino group, a ureido group, an imino group, a diazo group, an azo group, an azide group, and a diazoamino group are preferably used, and a cyano group is particularly preferred. Therefore, in a preferred embodiment of this embodiment, the binder of this embodiment contains a polymer having a cyano group, and in a more preferred embodiment of this embodiment, the binder of this embodiment contains a polymer having a cyano group and an acryloyl group and / or a methacryloyl group. This configuration can achieve a favorable balance between the formation of halogen bonds (and ion-dipole interactions) and the glass transition temperature (Tg) of the binder. Here, the glass transition temperature (Tg) of the polymer constituting the binder is not particularly limited, but is preferably −20° C. or lower, more preferably −25° C. or lower, even more preferably −30° C. or lower, particularly preferably −35° C. or lower, and most preferably −40° C. or lower. The lower limit of the glass transition temperature (Tg) of the polymer constituting the binder is also not particularly limited, but is usually −60° C. or higher. When the glass transition temperature (Tg) of the polymer constituting the binder is such a relatively low value, the polymer becomes flexible and mobile, allowing the polymer to exist with a wide spread in the layer containing it.As a result, it can more effectively contribute to the formation of the above-mentioned halogen bonds (and ion-dipole interactions).

[0054] The polymer described above can be obtained as a copolymer of a monomer containing (meth)acrylonitrile (containing a cyano group) and an alkyl (meth)acrylate. There are no particular limitations on the specific method for copolymerizing these monomers to obtain the copolymer, and conventionally known knowledge can be appropriately referred to. Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, tert-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, cyclohexyl (meth)acrylate, and 4-n-butylcyclohexyl (meth)acrylate. Among these, it is preferable to use at least 2-ethylhexyl acrylate (-70°C), isononyl acrylate (-58°C), n-butyl acrylate (-55°C), ethoxyethyl acrylate (-50°C), isoamyl acrylate (-45°C), and hexyl acrylate (-45°C) as alkyl (meth)acrylates, as these can lower the glass transition temperature (Tg) of the copolymer. In particular, 2-ethylhexyl acrylate and n-butyl acrylate are preferred because they are easily copolymerized, and 2-ethylhexyl acrylate is particularly preferred because of its low glass transition temperature.

[0055] Furthermore, the above-mentioned monomers may further contain a third monomer other than (meth)acrylonitrile and alkyl (meth)acrylate, and the specific form of such a third monomer can be determined by reference to conventionally known knowledge. However, the total proportion (copolymerization ratio) of (meth)acrylonitrile and alkyl (meth)acrylate in the monomers used to produce the copolymer is preferably 50% by mass, more preferably 80% by mass or more, even more preferably 85% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 99% by mass or more (the upper limit is 100% by mass). Furthermore, the proportion (copolymerization ratio) of (meth)acrylonitrile in the monomers used to produce the copolymer is preferably 20% by mass or more, more preferably 25% by mass or more. Meanwhile, the proportion (copolymerization ratio) of alkyl (meth)acrylate in the monomers used to produce the copolymer is preferably 80% by mass or less, more preferably 75% by mass or less. With this configuration, the above-described ion-dipole interaction can be made stronger when the binder according to the present embodiment is contained in the solid electrolyte layer, and the adhesion can be improved and the effect of preventing interfacial resistance can be made excellent.

[0056] The weight-average molecular weight (Mw) of the polymer constituting the binder according to the present invention is not particularly limited, but is preferably 100,000 or more, more preferably 200,000 or more, and even more preferably 300,000 or more. Meanwhile, the upper limit of the weight-average molecular weight (Mw) is also not particularly limited, and is typically 800,000 or less. If the weight-average molecular weight (Mw) is 100,000 or more, the binder molecules in the layer containing the binder according to the present invention will be more entangled, which can further improve interlayer adhesion and prevent interfacial resistance. In this specification, the weight-average molecular weight (Mw) of the polymer constituting the binder is measured by gel permeation chromatography (GPC) using a standard polystyrene equivalent. In a preferred embodiment of the secondary battery according to this aspect, the copolymerization ratio (mass ratio) of (meth)acrylonitrile in the copolymer constituting the binder is 25% or more, the glass transition point of the copolymer is −40° C. or less, and the weight average molecular weight (Mw) of the copolymer is 300,000 or more. This configuration makes it possible to achieve a more favorable balance between the formation of halogen bonds (and ion-dipole interactions) and the glass transition point (Tg) of the binder, and has the advantages of being particularly effective in improving interlayer adhesion and preventing interface resistance.

[0057] The amount of binder (polymer) contained in the positive electrode active material layer and / or solid electrolyte layer is not particularly limited, and the preferred amounts of binders in each layer described above can be similarly employed. Furthermore, the density of the binder according to this embodiment contained in the positive electrode active material layer and / or solid electrolyte layer preferably increases toward the interface between the positive electrode active material layer and the solid electrolyte layer. Examples of such a configuration include a positive electrode active material layer or solid electrolyte layer formed from multiple layers with different binder densities, with the layer with the higher binder density disposed at the interface. Furthermore, if possible, the density of the binder according to this embodiment may be continuously graded within a single-layer positive electrode active material layer or solid electrolyte layer so that it increases toward the interface. This configuration allows for efficient use of the binder according to this embodiment, which contributes to improving adhesion between layers, thereby reducing the amount of binder added and effectively contributing to improving the energy density of the battery.

[0058] [Negative electrode (negative electrode active material layer)] In the secondary battery according to this embodiment, the negative electrode active material layer 13 contains a negative electrode active material. The type of the negative electrode active material is not particularly limited, but examples thereof include carbon materials, metal oxides, and metal active materials. Examples of carbon materials include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Examples of metal oxides include Nb2O5, Li4Ti5O 12 and the like. Furthermore, silicon-based negative electrode active materials and tin-based negative electrode active materials may also be used. Here, silicon and tin belong to the 14th group of elements, and are known to be negative electrode active materials that can significantly improve the capacity of non-aqueous electrolyte secondary batteries. These simple substances can absorb and release a large number of charge carriers (lithium ions, etc.) per unit volume (mass), and therefore become high-capacity negative electrode active materials. Here, it is preferable to use Si simple substance as the silicon-based negative electrode active material. Similarly, SiO 2 disproportionated into two phases, an Si phase and a silicon oxide phase, is also used. xIt is also preferable to use silicon oxides such as (0.3≦x≦1.6). In this case, the range of x is more preferably 0.5≦x≦1.5, and even more preferably 0.7≦x≦1.2. Furthermore, an alloy containing silicon (silicon-containing alloy-based negative electrode active material) may be used. On the other hand, examples of negative electrode active materials containing tin element (tin-based negative electrode active materials) include simple Sn, tin alloys (Cu—Sn alloy, Co—Sn alloy), amorphous tin oxide, tin silicon oxide, etc. Among these, examples of amorphous tin oxide include SnB 0.4 P 0.6 O 3.1 Examples of tin silicon oxides include SnSiO3. A lithium-containing metal may also be used as the negative electrode active material. Such a negative electrode active material is not particularly limited as long as it is a lithium-containing active material, and examples thereof include lithium metal and lithium-containing alloys. Examples of lithium-containing alloys include alloys of Li with at least one of In, Al, Si, and Sn. In some cases, two or more negative electrode active materials may be used in combination. Of course, negative electrode active materials other than those listed above may also be used. The negative electrode active material preferably contains lithium metal, a lithium-containing alloy, a silicon-based negative electrode active material, or a tin-based negative electrode active material, and particularly preferably contains lithium metal or a lithium-containing alloy. When the negative electrode active material contains lithium metal or a lithium-containing alloy, the secondary battery according to this embodiment may be a so-called lithium deposition type in which lithium metal or a lithium-containing alloy is deposited on the negative electrode current collector during charging. In this case, a layer of lithium metal or a lithium-containing alloy deposited on the negative electrode current collector during charging serves as the negative electrode active material layer of the secondary battery according to this embodiment. Therefore, the thickness of the negative electrode active material layer increases with the progress of the charging process, and decreases with the progress of the discharging process. Although the negative electrode active material layer need not be present during full discharge, in some cases, a certain amount of the negative electrode active material layer made of lithium metal or a lithium-containing alloy may be present during full discharge.

[0059] The shape of the negative electrode active material may be, for example, particulate (spherical, fibrous), thin film, etc. When the negative electrode active material is particulate, the average particle diameter is, for example, preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, even more preferably in the range of 100 nm to 20 μm, and particularly preferably in the range of 1 to 20 μm.

[0060] The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably in the range of 40 to 99 mass %, more preferably in the range of 50 to 90 mass %. The negative electrode active material layer may further contain a solid electrolyte, a conductive additive, and / or a binder, and specific and preferred forms thereof may be the same as those described in the section on the positive electrode active material layer above.

[0061] The thickness of the negative electrode active material layer (in the case of a lithium deposition type secondary battery, the thickness when fully charged) differs depending on the configuration of the intended all-solid-state battery, but is preferably within the range of, for example, 0.1 to 1000 μm.

[0062] [Positive and negative current collector plates] The material constituting the current collector plates (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferred as constituent materials of the current collector plates. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The negative electrode current collector plate 25 and the positive electrode current collector plate 27 may be made of the same material or different materials.

[0063] [Positive and negative leads] Although not shown, the current collectors (11′, 11″) may be electrically connected to the current collector plates (25, 27) via negative and positive electrode leads. Materials used in known lithium ion secondary batteries may be used as the materials for the negative and positive electrode leads. The parts removed from the exterior are preferably covered with a heat-resistant, insulating heat-shrinkable tube or the like to prevent contact with peripheral devices or wiring, resulting in electrical leakage and affecting products (e.g., automobile parts, particularly electronic devices).

[0064] [Battery exterior materials] As the battery exterior material, a known metal can case can be used, or a bag-shaped case using an aluminum-containing laminate film 29 that can cover the power-generating element as shown in Figures 1 and 2 can be used. The laminate film can be, for example, a three-layer laminate film formed by laminating PP, aluminum, and nylon in this order, but is not limited to these. A laminate film is desirable from the viewpoint of achieving high output and excellent cooling performance, making it suitable for use in batteries for large devices such as EVs and HEVs. Furthermore, an aluminum-containing laminate film is more preferable for the exterior body because it allows for easy adjustment of the collective pressure applied to the power-generating element from the outside.

[0065] The stacked battery according to the present embodiment has a configuration in which a plurality of unit cell layers are connected in parallel, and therefore has high capacity and excellent cycle durability, and is therefore suitable for use as a driving power source for EVs and HEVs.

[0066] The above describes one embodiment of the secondary battery according to the present invention, but the present invention is not limited to the configuration described in the above embodiment, and can be modified as appropriate based on the claims.

[0067] For example, the secondary battery according to the present embodiment does not have to be an all-solid-state type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolytic solution). There is no particular limitation on the amount of liquid electrolyte (electrolytic solution) that can be contained in the solid electrolyte layer, but it is preferably an amount that allows the shape of the solid electrolyte layer formed by the solid electrolyte to be maintained and prevents leakage of the liquid electrolyte (electrolytic solution).

[0068] The liquid electrolyte (electrolytic solution) that can be used has a form in which a lithium salt is dissolved in an organic solvent. Examples of the organic solvent that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propionate (MP), methyl acetate (MA), methyl formate (MF), 4-methyldioxolane (4MeDOL), dioxolane (DOL), 2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), propylene carbonate (PC), butylene carbonate (BC), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL). Among these, from the viewpoint of further improving the rapid charging characteristics and output characteristics, the organic solvent is preferably a chain carbonate, more preferably at least one selected from the group consisting of diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC), and more preferably selected from ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

[0069] Examples of lithium salts include Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), Li(C2F5SO2)2N, LiPF6, LiBF4, LiClO4, LiAsF6, and LiCF3SO3. Among these, the lithium salt is preferably Li(FSO2)2N (LiFSI) from the viewpoints of battery output and charge / discharge cycle characteristics.

[0070] The liquid electrolyte (electrolytic solution) may further contain additives other than the above-mentioned components. Specific examples of such compounds include ethylene carbonate, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, vinyl ethylene carbonate, 1,2-divinyl ethylene carbonate, 1-methyl-1-vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1-ethyl-1-vinyl ethylene carbonate, and 1-ethyl-2-vinyl ethylene carbonate. Examples of the additive include ethylene carbonate, vinyl vinylene carbonate, allyl ethylene carbonate, vinyloxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acryloxymethyl ethylene carbonate, methacryloxymethyl ethylene carbonate, ethynyl ethylene carbonate, propargyl ethylene carbonate, ethynyloxymethyl ethylene carbonate, propargyloxyethylene carbonate, methylene ethylene carbonate, and 1,1-dimethyl-2-methylene ethylene carbonate. These additives may be used alone or in combination of two or more. The amount of additive used in the electrolyte solution can be adjusted as appropriate.

[0071] [Battery pack] A battery pack is made up of multiple batteries connected together. Specifically, it is made up of at least two batteries connected in series, parallel, or both. By connecting them in series or parallel, it is possible to freely adjust the capacity and voltage.

[0072] A small, detachable assembled battery can be formed by connecting multiple batteries in series or in parallel. Furthermore, a large-capacity, high-output assembled battery (such as a battery module or battery pack) can be formed by further connecting multiple such small, detachable assembled batteries in series or in parallel, suitable for use as a vehicle drive power source or auxiliary power source, which require high volumetric energy density and high volumetric power density. The number of batteries to be connected to form a battery assembly and the number of stacked small assembled batteries to form a large-capacity assembled battery can be determined based on the battery capacity and output of the vehicle (electric vehicle) in which the battery will be installed.

[0073] [vehicle] A battery or a battery pack formed by combining a plurality of such batteries can be mounted on a vehicle. The present invention makes it possible to construct a long-life battery with excellent long-term reliability. Therefore, by incorporating such a battery, a plug-in hybrid electric vehicle with a long EV driving range or an electric vehicle with a long driving range per charge can be constructed. For example, a battery or a battery pack formed by combining a plurality of such batteries can be used in a hybrid vehicle, a fuel cell vehicle, or an electric vehicle (all of which include four-wheeled vehicles (commercial vehicles such as passenger cars, trucks, and buses, and light vehicles), as well as two-wheeled vehicles (motorcycles) and three-wheeled vehicles) to produce a vehicle with a long life and high reliability. However, the application is not limited to automobiles, and the battery pack can also be applied to various power sources for other vehicles, such as trains, and can also be used as an on-board power source for uninterruptible power supplies and the like. [Example]

[0074] The present invention will be described in more detail below with reference to examples, although the technical scope of the present invention is not limited to the following examples.

[0075] <<Example of test cell production>> [Comparative Example 1] (Preparation of positive electrode) First, as the constituent material of the positive electrode active material layer, the positive electrode active material NMC composite oxide (composition = LiNi 0.8 Mn 0.1 Co 0.1The materials used were lithium ion conductive halogen-containing sulfide solid electrolyte (Argyrodite-type solid electrolyte (Li6PS5Cl)), acetylene black as a conductive additive, and styrene-butadiene rubber (SBR) as a binder. The weight-average molecular weight (Mw) of the SBR used as the binder was 300,000 as a standard polystyrene equivalent value determined by gel permeation chromatography (GPC), and the glass transition temperature (Tg) was -30°C.

[0076] Of these, NMC composite oxide, solid electrolyte, and acetylene black were weighed out to a mass ratio of 50:30:20 and mixed in an agate mortar in a glove box. The mixture was then further mixed and stirred in a planetary ball mill. Two parts by mass of styrene-butadiene rubber (SBR) was added to 100 parts by mass of the resulting mixed powder, and xylene was added as a solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry was then applied to one surface of a carbon-coated aluminum foil serving as a positive electrode current collector and dried to form a positive electrode active material layer (100 μm thick). A positive electrode was then fabricated.

[0077] Here, the average particle diameter of the secondary particles of the positive electrode active material (lithium-containing metal oxide) contained in the positive electrode active material layer of the obtained positive electrode and the average particle diameter of the primary particles constituting the secondary particles were measured by the following method, and were found to be 7.0 μm and 5.0 μm, respectively.

[0078] <Method for measuring average particle size> The cross-section of the prepared positive electrode active material layer was observed and evaluated using a scanning electron microscope (SEM) and an energy dispersive X-ray analyzer (EDX). The average particle size (arithmetic mean diameter) of the primary particles of the positive electrode active material was determined by measuring the particle diameter (the longest distance between any two points on the outline of the observed particle) of at least 50 particles that were visible in the cross-section of the positive electrode active material and did not have grain boundaries, and then calculating the arithmetic mean value. The average particle size (arithmetic mean diameter) of the secondary particles of the positive electrode active material was determined by measuring the particle diameter of at least 50 primary particles that did not have any other material between them, and then calculating the arithmetic mean value.

[0079] (Fabrication of solid electrolyte layer) The sulfide solid electrolyte prepared above and a binder (SBR) were mixed in a mass ratio of 95:5, and an appropriate amount of xylene was added as a solvent, followed by mixing to prepare a solid electrolyte slurry.

[0080] The solid electrolyte slurry prepared above was applied onto a stainless steel (SUS) foil serving as a negative electrode current collector, and the solvent was evaporated to form a solid electrolyte layer (thickness: 80 μm).

[0081] (Preparation of test cell) The solid electrolyte layer prepared above was transferred onto the exposed surface of the positive electrode prepared above by cold isostatic pressing (CIP).

[0082] Finally, an aluminum positive electrode tab and a nickel negative electrode tab were bonded to the carbon-coated aluminum foil serving as the positive electrode current collector and the SUS foil serving as the negative electrode current collector, respectively, using an ultrasonic welder. The resulting laminate was placed inside an aluminum laminate film and vacuum-sealed to produce a test cell for this comparative example.

[0083] [Example 1] Copolymer A of acrylonitrile (AN) and 2-ethylhexyl acrylate (EHA) (monomer composition ratio: AN:EHA = 25:75 (mass ratio)) was prepared as a binder. The weight average molecular weight (Mw) of copolymer A was 300,000 as a standard polystyrene equivalent value measured by gel permeation chromatography (GPC), and the glass transition temperature (Tg) was -40°C.

[0084] A test cell of this example was produced in the same manner as in Comparative Example 1 described above, except that copolymer A was used instead of SBR as the binder contained in both the positive electrode active material layer and the solid electrolyte layer.

[0085] [Example 2] As a binder, a copolymer B of acrylonitrile (AN) and 2-ethylhexyl acrylate (EHA) (monomer composition ratio: AN:EHA = 20:80 (mass ratio)) was prepared. The weight average molecular weight (Mw) of copolymer B was 300,000 as a standard polystyrene equivalent value determined by gel permeation chromatography (GPC), and the glass transition temperature (Tg) was -45°C.

[0086] A test cell of this example was produced in the same manner as in Comparative Example 1 described above, except that copolymer B was used instead of SBR as the binder contained in both the positive electrode active material layer and the solid electrolyte layer.

[0087] [Example 3] A copolymer C of acrylonitrile (AN), 2-ethylhexyl acrylate (EHA), and methyl methacrylate (AN:EHA = 20:80 (mass ratio)) was prepared as a binder. The weight-average molecular weight (Mw) of copolymer C was 300,000 as calculated by gel permeation chromatography (GPC) using standard polystyrene standards, and its glass transition temperature (Tg) was -25°C.

[0088] A test cell of this example was produced in the same manner as in Comparative Example 1 described above, except that copolymer C was used instead of SBR as the binder contained in both the positive electrode active material layer and the solid electrolyte layer.

[0089] [Example 4] A copolymer D of acrylonitrile (AN) and 2-ethylhexyl acrylate (EHA) (monomer composition ratio: AN:EHA = 25:75 (mass ratio)) was prepared as a binder. The weight average molecular weight (Mw) of copolymer D was 50,000 as calculated by gel permeation chromatography (GPC) using standard polystyrene standards, and the glass transition temperature (Tg) was -40°C.

[0090] A test cell of this example was produced in the same manner as in Comparative Example 1 described above, except that copolymer D was used instead of SBR as the binder contained in the positive electrode active material layer and the solid electrolyte layer.

[0091] [Example 5] As the positive electrode active material, NMC composite oxide (composition: LiNi 0.6 Mn 0.2 Co 0.2 O2) was prepared.

[0092] The positive electrode active material contained in the positive electrode active material layer is LiNi 0.8 Mn 0.1 Co 0.1 LiNi instead of O2 0.6 Mn 0.2 Co 0.2 A test cell of this example was fabricated in the same manner as in Example 1 above, except that O2 was used.

[0093] [Example 6] As the binder, the same copolymer A as in Example 1 was prepared.

[0094] A test cell of this example was produced in the same manner as in Comparative Example 1 above, except that Copolymer A was used instead of SBR as the binder contained in the solid electrolyte layer.

[0095] The specifications of the binders used in the above-mentioned Examples and Comparative Examples are shown in Table 1 below.

[0096] [Table 1]

[0097] <Test cell evaluation example> (Evaluation of adhesion at the interface between the positive electrode active material layer and the solid electrolyte layer) A laminate of a positive electrode current collector / positive electrode active material layer / solid electrolyte layer / negative electrode current collector prepared in the same manner as in the above-described test cell preparation example was used, and one side was fixed to a stand using double-sided tape. A 90° peel test was then performed at a peel rate of 50 mm / min, and the peel strength when the interface between the positive electrode active material layer and the solid electrolyte layer peeled off was measured. The results are shown in Table 2 below. The peel strength values ​​shown in Table 2 are relative values, with Comparative Example 1 set to 100.

[0098] (Evaluation of internal resistance after cycle charge / discharge) A pressure of 5 MPa was applied to the test cell in the stacking direction using a pressure member. Under this condition, the upper and lower voltage limits were set to 3.0 to 4.3 V at a temperature of 60°C, and 10 charge-discharge cycles were performed at a current equivalent to 0.05 C in C-rate terms.

[0099] The battery was then charged to 100% SOC at a temperature of 60°C, and discharged repeatedly under the following conditions. The current and voltage drop were plotted. The internal resistance during discharge was calculated from the slope of the plotted graph. The results are shown in Table 2 below. The internal resistance values ​​shown in Table 2 are relative values, with Comparative Example 1 set to 100.

[0100] <Conditions for discharge treatment> 0.05C CC discharge (15 seconds) ⇒ 2 hour rest ⇒ 0.1C CC discharge (15 seconds) ⇒ 2 hour rest ⇒ 0.2C CC discharge (15 seconds) ⇒ 2 hour rest ⇒ 0.5C CC discharge (15 seconds).

[0101] [Table 2]

[0102] The results shown in Table 1 show that by including a solid electrolyte containing a halogen element in one of the positive electrode active material layer and the solid electrolyte layer, and including a binder having a functional group with an unshared electron pair in the other, in a secondary battery using an NMC composite oxide having a specified average particle size and composition as the positive electrode active material, the adhesion between the positive electrode active material layer and the solid electrolyte layer can be improved, and as a result, the internal resistance of the battery can be reduced.

[0103] In particular, Example 1, which uses copolymer A, in which the copolymerization ratio (mass ratio) of (meth)acrylonitrile in the copolymer is 25% or more, the copolymer has a glass transition temperature of -40°C or less, and the copolymer has a weight average molecular weight (Mw) of 300,000 or more, is found to be particularly excellent in improving interlayer adhesion and preventing interfacial resistance. This is thought to be because such a configuration achieves a favorable balance between the formation of halogen bonds (and ion-dipole interactions) and the glass transition temperature (Tg) of the binder.

[0104] In addition, the general formula (1) (Li a Ni b Mn c Co d M x It can be seen that in Example 5, where the value of b in O2) satisfies 0.6≦b≦0.7, the above-mentioned effects are further improved compared to Example 1. [Explanation of symbols]

[0105] 10a, 100 stacked battery, 11' negative electrode current collector, 11” positive electrode current collector, 13 negative electrode active material layer, 15 positive electrode active material layer, 17 solid electrolyte layer, 19 cell layer, 21 power generation elements, 25 negative current collector plate, 27 positive current collector plate, 29 Laminating film, 200 metal plate, 300 volts, 400 Nuts.

Claims

1. a positive electrode including a positive electrode active material layer containing a positive electrode active material made of secondary particles; a negative electrode; a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; A secondary battery having a power generating element comprising: The positive electrode active material is Li(Ni—Mn—Co)O ２ Alternatively, the present invention includes an NMC composite oxide having a composition in which a part of these transition metals is substituted with other elements, the average particle size of the secondary particles is 15.0 μm or less, and the average particle size of the primary particles constituting the secondary particles is 0.5 μm or more, at least one of the positive electrode active material layer and the solid electrolyte layer contains a solid electrolyte containing a halogen element, and the other contains a binder having a functional group having an unshared electron pair; a secondary battery in which the binder contains a copolymer of monomers consisting of (meth)acrylonitrile and 2-ethylhexyl (meth)acrylate, a copolymerization ratio (mass ratio) of the (meth)acrylonitrile in the copolymer is 25 mass % or more, a glass transition point of the copolymer is −20° C. or less, and a weight average molecular weight (Mw) of the copolymer is 100,000 or more.

2. 2. The secondary battery according to claim 1, wherein the positive electrode active material layer contains the solid electrolyte containing the halogen element, and the solid electrolyte layer contains the binder.

3. 3. The secondary battery according to claim 1, wherein both the positive electrode active material layer and the solid electrolyte layer contain the halogen-containing solid electrolyte and the binder.

4. 4. The secondary battery according to claim 1, wherein the density of the binder contained in the positive electrode active material layer and / or the solid electrolyte layer increases toward the interface between the positive electrode active material layer and the solid electrolyte layer.

5. The NMC composite oxide is represented by the following general formula (1): General formula (1): Li ａ Ni ｂ Mn ｃ Co ｄ M ｘ O ２ In the formula, a, b, c, d, and x satisfy the following conditions: 0.98≦a≦1.2, 0.6≦b≦0.9, 0<c≦0.4, 0<d≦0.4, 0≦x≦0.3, and b+c+d+x=1. M is at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr. The secondary battery according to any one of claims 1 to 4, having a composition represented by the formula:

6. The secondary battery according to claim 5 , wherein b satisfies 0.6≦b≦0.

7.

7. 7. The secondary battery according to claim 1, wherein the solid electrolyte containing a halogen element is a sulfide solid electrolyte containing a halogen element.

8. The secondary battery according to any one of claims 1 to 7, which is an all-solid-state lithium secondary battery.

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