Battery

Abstract

To provide a battery capable of suppressing reduction in energy density.SOLUTION: The battery includes an electrode body formed by laminating a positive electrode current collector, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer, and a negative electrode current collector, wherein a spring constant in a lamination direction of the electrode body is 27000 kN / cm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to batteries. [Background technology]

[0002] Patent Document 1 discloses that the power generating element of an all-solid-state battery is covered with an elastic body having a lower Young's modulus than the solid electrolyte, thereby absorbing expansion and contraction during charging and discharging. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-108509 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when an elastic body is used in this way, the elastic body occupies a part of the battery, which reduces the volume of the battery element by that amount, resulting in a decrease in energy density.

[0005] Therefore, an object of the present disclosure is to provide a battery that can suppress a decrease in energy density. [Means for solving the problem]

[0006] The present application discloses a battery including an electrode body formed by stacking a positive electrode current collector, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer, and a negative electrode current collector, wherein the spring constant in the stacking direction of the electrode body is 27,000 kN / cm or less.

[0007] The filling rate of the negative electrode active material layer may be 80% or less.

[0008] The active material of the negative electrode active material layer may be Si, and the Si may be particles coated with a binder contained in the negative electrode active material layer.

[0009] The active material of the negative electrode active material layer may be a Si alloy, and the Si alloy may be made porous, with the pore volume being 0.3 mL / g.

[0010] The solid electrolyte contained in the solid electrolyte layer may be a sulfide or an organic polymer.

[0011] The negative electrode current collector may be an aluminum foil. [Effects of the Invention]

[0012] According to the battery of the present disclosure, the proportion of the elastic body in the total volume of the battery can be reduced, and a decrease in the energy density of the battery due to the elastic body can be suppressed. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating the layer structure of an all-solid-state battery. [Figure 2] FIG. 2 is a diagram illustrating the measurement of the spring constant of the electrode body. DETAILED DESCRIPTION OF THE INVENTION

[0014] 1. Battery configuration FIG. 1 illustrates a diagram of a solid-state battery (all-solid-state battery) according to one embodiment. Here, an all-solid-state battery is used as a typical example for the description, but the present disclosure is not necessarily limited to all-solid-state batteries and can be applied to any battery having an electrode body and an exterior body that seals it (e.g., a solid-state battery (semi-solid battery) that contains a solid electrolyte and an electrolytic solution). FIG. 1 illustrates the layer structure of an electrode body 11 included in a solid-state battery. A solid-state battery is formed by sealing such an electrode body 11 in an exterior body. For example, an electrode body 11 that is roughly rectangular in plan view is enclosed in an exterior body that is also roughly rectangular in plan view. In this case, a positive terminal extends from the positive electrode current collector of the electrode body 11, and a negative terminal extends from the negative electrode current collector, with their tips protruding from the exterior body. The components of the laminate 11 and their relationships will be described in more detail below.

[0015] The electrode body 11 has a positive electrode current collector 12, a positive electrode active material layer 13, a solid electrolyte layer 14, a negative electrode active material layer 15, and a negative electrode current collector 16. In this embodiment, the positive electrode current collector 12, the positive electrode active material layer 13, the solid electrolyte layer 14, the negative electrode active material layer 15, and the negative electrode current collector 16 are stacked in this order to form a unit element 11a, and a plurality of unit elements 11a are stacked to form the electrode body 11 (only one unit element 11a is shown in FIG. 1). As described above, a positive electrode terminal is electrically connected to the positive electrode current collector 12 of the electrode body 11, and a negative electrode terminal is electrically connected to the negative electrode current collector 16 of the electrode body 11.

[0016] 1.1. Positive electrode current collector The positive electrode current collector 12 is laminated on the positive electrode active material layer 13 to collect current from the positive electrode active material layer 13. In this embodiment, the positive electrode current collector 12 is a rectangular foil in plan view, and can be composed of a positive electrode current collector foil, which is a metal foil, and a conductive resin layer or a carbon layer laminated on the positive electrode current collector foil. The conductive resin layer or the carbon layer is laminated on the positive electrode active material layer 13, thereby laminating the positive electrode current collector 12 on the positive electrode active material layer 13. Examples of materials constituting the positive electrode current collector include metal foil materials such as stainless steel, aluminum, nickel, iron, and titanium, conductive resin layers made of resins in which conductive materials are dispersed, and carbon layers made of materials containing carbon.

[0017] 1.2. Positive electrode active material layer The positive electrode active material layer 13 has the positive electrode current collector 12 laminated on one surface and the solid electrolyte layer 14 laminated on the other surface. In this embodiment, the positive electrode active material layer 13 has a rectangular sheet shape in plan view.

[0018] The positive electrode active material layer 13 is a layer containing a positive electrode active material, and may further contain at least one of a solid electrolyte material, a conductive material, and a binder, as necessary. The positive electrode active material may be a known active material. Examples include cobalt-based (LiCoO2, etc.), nickel-based (LiNiO2, etc.), manganese-based (LiMn2O4, Li2Mn2O3, etc.), iron phosphate-based (LiFePO4, Li2FeP2O7, etc.), NCA-based (nickel, cobalt, aluminum compound), and NMC-based (nickel, manganese, cobalt compound). More specifically, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and others. The surface of the positive electrode active material may be coated with an oxide layer such as a lithium niobate layer, a lithium titanate layer, or a lithium phosphate layer. Furthermore, the positive electrode active material is not limited to the oxides mentioned above, and may be a sulfide-based material (lithium titanium sulfide, lithium niobium sulfide).

[0019] The solid electrolyte may be an inorganic solid electrolyte. Inorganic solid electrolytes have higher ionic conductivity and better heat resistance than organic polymer electrolytes. Examples of inorganic solid electrolytes include sulfide solid electrolytes and oxide solid electrolytes. Examples of sulfide solid electrolyte materials having Li ion conductivity include 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, Li2S-P2S5-ZmSn (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, and 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 above description of "Li2S-P2S5" means a sulfide solid electrolyte material obtained using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions. From the viewpoint of reducing the spring constant of the present disclosure, a sulfide solid electrolyte is more preferable than an oxide solid electrolyte.

[0020] On the other hand, examples of oxide solid electrolyte materials having Li ion conductivity include compounds having a NASICON structure. An example of a compound having a NASICON structure is a compound represented by the general formula Li 1+x AlxGe 2-x Compounds (LAGP) represented by (PO4)3 (0≦x≦2), general formula Li 1+x Al x Ti 2-x Examples of the oxide solid electrolyte material include a compound (LATP) represented by (PO4)3 (0≦x≦2). 0.34 La 0.51 TiO3), LiPON (e.g., Li 2.9 PO 3.3 N 0.46 ), LiLaZrO (e.g., Li7La3Zr2O 12 ) etc.

[0021] However, from the viewpoint of reducing the spring constant of the present disclosure, an organic polymer electrolyte may be used, or the inorganic solid electrolyte and the organic polymer electrolyte may be used in combination. The polymer electrolyte contains at least a polymer component. Examples of the polymer component include polyether-based polymers, polyester-based polymers, polyamine-based polymers, and polysulfide-based polymers. Among these, polyether-based polymers are preferred because they have high ionic conductivity and excellent mechanical properties such as Young's modulus and breaking strength.

[0022] The polyether-based polymer has a polyether structure in the repeating unit. The polyether-based polymer preferably has a polyether structure in the main chain of the repeating unit. Examples of the polyether structure include a polyethylene oxide (PEO) structure and a polypropylene oxide (PPO) structure. The polyether-based polymer preferably has a PEO structure as the main repeating unit. In the polyether-based polymer, the proportion of the PEO structure in all repeating units is, for example, 50 mol % or more, or may be 70 mol % or more, or may be 90 mol % or more. The polyether-based polymer may also be, for example, a homopolymer or copolymer of an epoxy compound (e.g., ethylene oxide, propylene oxide).

[0023] The polymer component may have the following ion-conducting units: Examples of the ion-conducting units include polyethylene oxide, polypropylene oxide, polymethacrylic acid ester, polyacrylic acid ester, polydimethylsiloxane, polyacrylic acid, polymethacrylic acid, polyethylene vinyl acetate, polyimide, polyamine, polyamide, polyalkyl carbonate, polynitrile, polyphosphazene, polyolefin, and polydiene.

[0024] The weight-average molecular weight (Mw) of the polymer component is not particularly limited, but is, for example, 1,000,000 or more and 10,000,000 or less. Mw is determined by gel permeation chromatography (GPC). The glass transition temperature (Tg) of the polymer component is, for example, 60°C or less, or may be 40°C or less, or may be 25°C or less. The polymer electrolyte may contain only one type of polymer component, or may contain two or more types. The polymer electrolyte may be a crosslinked polymer electrolyte in which the polymer component is crosslinked, or an uncrosslinked polymer electrolyte in which the polymer component is not crosslinked.

[0025] The polymer electrolyte may be a dry polymer electrolyte or a gel electrolyte. A dry polymer electrolyte refers to an electrolyte having a solvent component content of 5% by weight or less. The solvent component content may be 3% by weight or less, or may be 1% by weight or less. Note that when a sulfide solid electrolyte that is highly reactive with polar solvents is used in the positive electrode active material layer, a dry polymer electrolyte is preferred.

[0026] The dry polymer electrolyte may contain a supporting salt. Examples of supporting salts include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6, and organic lithium salts such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3. The ratio of the supporting salt to the dry polymer electrolyte is not particularly limited. For example, when the dry polymer electrolyte has EO units (C2H5O units), the EO units may be, for example, 5 molar parts or more, 10 molar parts or more, or even 15 molar parts or more per 1 molar part of the supporting salt. On the other hand, the EO units may be, for example, 40 molar parts or less, or even 30 molar parts or less per 1 molar part of the supporting salt.

[0027] Gel electrolytes typically contain an electrolyte solution component in addition to a polymer component. The electrolyte solution component contains a supporting salt and a solvent. The supporting salt is the same as described above. Examples of the solvent include carbonates. Examples of carbonates include cyclic esters (cyclic carbonates) such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC); and chain esters (chain carbonates) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Examples of the solvent include acetates such as methyl acetate and ethyl acetate, and ethers such as 2-methyltetrahydrofuran. Examples of the solvent include γ-butyrolactone, sulfolane, N-methylpyrrolidone (NMP), and 1,3-dimethyl-2-imidazolidinone (DMI). The solvent may also be water.

[0028] The binder is not particularly limited as long as it is chemically and electrically stable, and examples thereof include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), rubber-based binders such as styrene butadiene rubber (SBR), olefin-based binders such as polypropylene (PP) and polyethylene (PE), and cellulose-based binders such as carboxymethyl cellulose (CMC). As the conductive material, carbon materials such as acetylene black (AB), ketjen black, and carbon fiber, and metal materials such as nickel, aluminum, and stainless steel can be used.

[0029] The content of each component in the positive electrode active material layer 13 may be the same as in the past. The thickness of the positive electrode active material layer 13 is, for example, preferably 0.1 μm to 1 mm, and more preferably 1 μm to 150 μm.

[0030] 1.3.Solid electrolyte layer In this embodiment, the solid electrolyte layer (separator layer) 14 is a rectangular sheet in plan view, and is disposed between the positive electrode active material layer 13 and the negative electrode active material layer 15. The solid electrolyte layer 14 contains at least a solid electrolyte material. The solid electrolyte material can be considered to be the same as the solid electrolyte material described for the positive electrode active material layer 13.

[0031] 1.4.Negative electrode active material layer The negative electrode active material layer 15 is a layer containing at least a negative electrode active material. The negative electrode active material layer 15 may contain a binder, a conductive material, and a solid electrolyte material as needed. The binder, conductive material, and solid electrolyte material can be considered to be similar to those of the positive electrode active material layer 13.

[0032] The negative electrode active material is not particularly limited, but in the case of constructing a lithium ion battery, examples of the negative electrode active material include carbon materials such as graphite and hard carbon, various oxides such as lithium titanate, Si and Si alloys, metallic lithium and lithium alloys, and the like.

[0033] In this embodiment, the negative electrode active material layer 15 is in the form of a rectangular sheet in plan view, with the solid electrolyte layer 14 laminated on one surface and the negative electrode current collector 16 laminated on the other surface. The content of each component in the negative electrode active material layer 15 may be the same as in the past. The thickness of the negative electrode active material layer 15 is, for example, preferably 0.1 μm to 1 mm, more preferably 1 μm to 150 μm.

[0034] 1.5. Negative electrode current collector The negative electrode current collector 16 is laminated on the negative electrode active material layer 15 to collect current from the negative electrode active material layer 15. In this embodiment, the negative electrode current collector 16 has a rectangular foil shape in a plan view, and can be made of, for example, stainless steel, copper, nickel, carbon, aluminum, or the like.

[0035] 1.6. Positive and negative terminals The positive electrode terminal and the negative electrode terminal are electrically conductive members, and serve as terminals for electrically connecting each electrode to the outside. One end of the positive electrode terminal is electrically connected to the positive electrode current collector 12, and the other end penetrates the exterior body and is exposed to the outside. One end of the negative electrode terminal is electrically connected to the negative electrode current collector 16, and the other end passes through the exterior body and is exposed to the outside.

[0036] 1.7.Exterior body The exterior body is made of a rectangular sheet-like member in a plan view, and includes, for example, a first sheet and a second sheet. The electrode assembly 11 is enclosed between the first sheet and the second sheet, and the outer peripheral edge of the first sheet and the outer peripheral edge of the second sheet are joined and sealed. Therefore, this exterior body is bag-shaped, and the electrode assembly 11 is enclosed and sealed inside.

[0037] The first and second sheets can be made of a laminate film. Here, a laminate film is a film having a metal layer and a sealant layer. Examples of metals used in the laminate film include aluminum and stainless steel, and examples of materials used in the sealant layer include thermoplastic resins such as polypropylene, polyethylene, polystyrene, and polyvinyl chloride.

[0038] 1.8. Spring constant of the electrode body The electrode assembly 11, formed by stacking the layers as described above, has a spring constant of 27,000 kN / cm or less in the stacking direction for the unit elements 11a. This allows the electrode layer 11 to easily deform elastically, absorbing expansion and contraction that occurs during charging and discharging of the battery. This eliminates the need for elastic bodies, or reduces the amount of elastic bodies added to the electrode assembly 11, if any. This also reduces the proportion of elastic bodies in the battery's volume, allowing for more battery elements (unit elements) to be arranged, thereby increasing the energy density of the battery. The spring constant value of the unit elements 11a in the stacking direction can be obtained as described later in the Examples. The spring constant should be 27,000 kN / cm or less, but a smaller spring constant can further reduce the occupancy rate of the elastic body and increase the energy density, so it is preferably 25,000 kN / cm or less, and more preferably 22,000 kN / cm or less. The lower limit of the spring constant is not particularly limited, but it is preferably 8,000 kN / cm. If it is less than 8,000 kN / cm, it may be difficult to construct a solid-state battery. It is more preferably 11,000 kN / cm or more.

[0039] The spring constant of the electrode assembly can be adjusted by any of the following methods, including [Mode 1] to [Mode 5]. Any of these modes, a combination of multiple modes, or other modes may also be used.

[0040] [Aspect 1] Although the layers described above are usually pressed at elevated temperatures when stacking, they are stacked at room temperature or at a lower temperature to adjust the spring constant, which makes it easier for voids to form in the electrode body and makes it possible to keep the spring constant low. For example, this allows the porosity of the negative electrode active material layer to be 20% or more (filling rate of 80% or less), thereby keeping the spring constant low. From the viewpoint of battery performance, it is preferable that the filling rate of the positive electrode active material layer is 80% or more. Instead of or in addition to setting the temperature to room temperature or lower than normal, the spring constant can also be kept low by lowering the pressing pressure below normal.

[0041] [Aspect 2] When Si is used as the negative electrode active material, the Si is coated with a binder (granules) to reduce the spring constant of the electrode body 11. This is thought to be because the gap between the Si surface and the coating layer contributes to the reduction in the spring constant.

[0042] [Aspect 3] When a Si alloy is used as the negative electrode active material, the spring constant can be kept low by making the Si alloy porous. Specifically, the pore volume is preferably 0.3 mL / g or more.

[0043] [Aspect 4] The spring constant of the electrode body can be reduced by using a material with a low modulus of elasticity (Young's modulus) for the negative electrode current collector 16. For example, the negative electrode body, which is normally made of nickel foil, can be changed to aluminum foil. This makes it possible to keep the spring constant of the electrode body 11 as a whole low.

[0044] [Aspect 5] By using a sulfide solid electrolyte or an organic polymer electrolyte as the solid electrolyte in the solid electrolyte layer, the spring constant can be kept lower than that of an oxide solid electrolyte. [Example]

[0045] 2. Working Example In the examples, tests were carried out by changing the spring constant in the stacking direction of the electrode body.

[0046] 2.1. Preparation of the electrode body [Forming the positive electrode active material layer] The positive electrode active material, sulfide solid electrolyte, conductive material, and binder were weighed out and molded in a mass ratio of positive electrode active material:sulfide solid electrolyte:conductive material:binder=85:13:1.3:0.7, to obtain a positive electrode active material layer. The cathode active material used was NCA (manufactured by Sumitomo Metal Mining Co., Ltd.) coated with oxide. The sulfide solid electrolyte was synthesized from 10LiI-90 (0.75Li2S-0.25P2S5), which was crystallized and micronized. The conductive material was vapor-grown carbon fiber (VGCF, manufactured by Showa Denko K.K.). The binder was PVDF.

[0047] [Forming the solid electrolyte layer] The same sulfide solid electrolyte as that used in the positive electrode active material layer and a binder were mixed in a mass ratio of 99.6:0.4 to prepare a solid electrolyte mixture, and the obtained solid electrolyte mixture was molded to obtain a solid electrolyte layer (thickness: 15 μm).

[0048] [Forming of negative electrode active material layer] The negative electrode active material, sulfide solid electrolyte, conductive material, and binder were weighed out and molded in a mass ratio of negative electrode active material:sulfide solid electrolyte:conductive material:binder=53:41:4.5:1.5 to obtain a negative electrode active material layer. The negative electrode active material used was Si (manufactured by Mitsui Kinzoku Co., Ltd., average particle diameter D50=2.5 ​​μm). The sulfide solid electrolyte, conductive material, and binder were the same as those used in the positive electrode active material layer. Here, the average particle diameter D50 is the volume-based median diameter measured by laser diffraction / scattering particle size distribution measurement. The median diameter (D50) is the diameter (volume average diameter) at which the cumulative volume of particles is half (50%) of the total when arranged in order from smallest to largest particle size.

[0049] [Preparing the current collector] A laminate of metal foil (aluminum, 12 μm thick) and conductive resin (acrylic resin, 2 μm thick) was prepared as the positive electrode current collector, and nickel (Ni) foil (10 μm thick) was prepared as the negative electrode current collector.

[0050] [Fabrication of solid-state batteries] By stacking the layers described above, a reference electrode body (comparative example) having a layer structure of positive electrode current collector / positive electrode active material layer / solid electrolyte layer / negative electrode active material layer / negative electrode current collector was obtained. The layers were stacked so that the conductive resin of the positive electrode current collector was in contact with the positive electrode active material layer. During stacking, the layers were heated and pressed at 170°C under a pressure of 11.2 MPa.

[0051] [Example 1] In Example 1, in order to adjust the spring constant in the lamination direction of the electrode body, the layers were laminated at room temperature without heating. [Example 2] In Example 2, in order to adjust the spring constant in the stacking direction of the electrode body, Si was used as the negative electrode active material, and granules in which Si particles were coated with a binder were used. [Example 3] In Example 3, in order to adjust the spring constant in the stacking direction of the electrode body, a foil made of aluminum (Al) was used as the negative electrode current collector instead of Ni. [Example 4] In Example 4, the pressing pressure was set smaller than in the other Examples in order to adjust the spring constant in the stacking direction of the electrode body. [Example 5] In Example 5, the pressing pressure was set smaller than that in Example 4 in order to adjust the spring constant in the stacking direction of the electrode body.

[0052] 2.2. Measuring the spring constant As shown in Figure 2, the electrode was placed in a jig between pressure plates and installed in an autograph (Shimadzu Corporation, AG-X50kN). A load was applied to the electrode with the pressure plates, and the displacement was measured with a displacement meter. The force at that time was measured with a load cell, and the Young's modulus (spring constant) was calculated from the relationship between stress and strain. The autograph head speed was 0.15 mm / min, and the load range was 0 kN to 49 kN. In this example, the SOC (state of charge) of the battery was set to 0%.

[0053] In this example, an electrode body consisting of one unit element was obtained and the spring constant was measured as described above, but the spring constant of an electrode body consisting of multiple unit elements may also be measured as described above and converted to a spring constant per unit element (this can be thought of as multiple unit elements connected in series).

[0054] 2.3.Results In addition to the spring constant, the elastic body occupancy rate and the increase in energy density were calculated. The elastic body occupancy rate was calculated by calculating the size of the additional elastic body required to obtain the spring constant normally required for the entire battery from the spring constant obtained by measurement, and expressing the ratio of the elastic body to the entire battery as a percentage. The increase in energy density was calculated by calculating the electrical energy density during charging and discharging of the battery, and the increase was expressed as a percentage when the reference value (comparison example) was set to 0. Furthermore, the charge / discharge performance of each example is shown as "performance as a battery" when the comparative example is set at 100.

[0055] [Table 1]

[0056] As can be seen from the results, by keeping the spring constant low, the occupancy rate of the elastic body can be reduced, and the energy density can be increased. Although this example shows the results when the SOC is 0%, the spring constant can be obtained in a similar range even when the battery is in a charged state. For example, in Example 3, when the SOC is 50%, the spring constant is 19570 kN / cm, and the effect is in the same range as when the SOC is 0%. [Explanation of symbols]

[0057] 11…Electrode body, 12…Positive current collector, 13…Positive active material layer, 14…Solid electrolyte layer, 15…Negative active material layer, 16…Negative current collector

Claims

1. A battery including an electrode assembly formed by laminating a positive electrode current collector, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer, and a negative electrode current collector, The spring constant in the stacking direction of the electrode body is 27000 kN / cm or less. battery.

2. The battery according to claim 1 , wherein the packing ratio of the negative electrode active material layer is 80% or less.

3. 2. The battery according to claim 1, wherein the active material of the negative electrode active material layer is Si, and the Si is in the form of particles coated with a binder contained in the negative electrode active material layer.

4. 2. The battery according to claim 1, wherein the active material of the negative electrode active material layer is a Si alloy, the Si alloy is made porous, and the pore volume of the Si alloy is 0.3 mL / g.

5. 2. The battery according to claim 1, wherein the solid electrolyte contained in the solid electrolyte layer is a sulfide or an organic polymer.

6. 2. The battery of claim 1, wherein the negative electrode current collector is aluminum foil.

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