battery cell

Abstract

To provide a battery cell capable of suppressing dendrite precipitation and improving cycle characteristics.SOLUTION: A battery cell includes a negative electrode layer, an electrolyte layer, and a positive electrode layer, where a negative electrode active material layer in the negative electrode layer has a recess and a flat part on the surface on the electrolyte layer side, and the recess is a cone-shaped recess with an inclined portion. It is preferable that the negative electrode active material layer contains lithium metal, and the electrolyte layer is a solid electrolyte layer containing a solid electrolyte. When there are a plurality of recesses, it is preferable that the plane portions are formed between the plurality of recesses.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a battery cell. [Background technology]

[0002] Traditionally, secondary batteries such as lithium-ion batteries, which have high energy density, have been widely used. In recent years, the use of secondary batteries has been considered in various applications, such as in automobiles, from the perspectives of improving energy efficiency, mitigating adverse impacts on the global environment by increasing the proportion of renewable energy, and reducing CO2 emissions. A secondary battery has a structure in which a solid electrolyte (separator) is present between the positive electrode and the negative electrode, and the battery is filled with a liquid or solid electrolyte (electrolyte solution).

[0003] The negative electrode active material of secondary batteries is typically a metal such as lithium metal. However, when lithium metal is used as the negative electrode active material, the formation of dendrites can cause short circuits, which is a significant problem. In particular, in solid-state batteries with a solid electrolyte, short circuits can occur if there is an imbalance in the restraining load.

[0004] As a lithium secondary battery anode in which the growth of dendrite crystals is suppressed, for example, a technique is known in which a large number of crystal nuclei, which serve as crystal growth points, are formed on the anode to generate a large number of crystals and suppress the formation of large dendrite crystals (see Patent Document 1). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-84512 [Overview of the project] [Problems that the invention aims to solve]

[0006] The technology disclosed in Patent Document 1 forms fine irregularities on the substrate surface to suppress the generation of large dendrite crystals. However, for example, when applying the above technology to a solid battery, as a result of applying a strong restraint load to the electrode, even the generation of relatively small dendrite crystals may affect the battery performance. Therefore, at present, favorable cycle characteristics accompanying the charge and discharge of the battery cell have not been obtained.

[0007] The present invention has been made in view of the above, and an object thereof is to provide a battery cell that can suppress the precipitation of dendrites and improve cycle characteristics.

Means for Solving the Problems

[0008] (1) The present invention relates to a battery cell having a negative electrode layer, an electrolyte layer, and a positive electrode layer, wherein the negative electrode active material layer in the negative electrode layer has concave portions and flat portions on the surface on the electrolyte layer side, and the concave portions are conical concave portions having inclined portions.

[0009] (1) According to the invention of (1), a battery cell capable of suppressing the precipitation of dendrites and improving cycle characteristics can be provided.

[0010] (2) The battery cell according to (1), wherein the negative electrode active material layer contains lithium metal.

[0011] (2) According to the invention of (2), even when lithium metal, which is likely to generate dendrites, is used as the negative electrode active material, the occurrence of a short circuit can be suppressed, and a battery cell having favorable cycle characteristics can be provided.

[0012] (3) The battery cell according to (1) or (2), wherein the electrolyte layer is a solid electrolyte layer containing a solid electrolyte.

[0013] (3) According to the invention of (3), even a battery cell having a solid electrolyte layer containing a solid electrolyte as the electrolyte layer can suppress the occurrence of a short circuit and provide a battery cell having favorable cycle characteristics.

[0014] (4) A plurality of the concave portions are formed, and the flat portions are respectively formed between the plurality of concave portions. The battery cell according to any one of (1) to (3).

[0015] According to the invention of (4), even when a plurality of concave portions are formed in the negative electrode active material, since no convex portion is formed on the electrolyte layer side, dendrites can be preferentially generated in the concave portions, and the occurrence of short circuit in the battery cell can be more preferably suppressed.

Brief Description of the Drawings

[0016] [Figure 1] It is a cross-sectional view showing the configuration of a battery cell according to an embodiment of the present invention. [Figure 2] It is a top view showing a part of a negative electrode active material layer according to an embodiment of the present invention. [Figure 3] It is a graph showing the results of a cycle characteristic test using the battery cells of Examples and Comparative Examples.

Modes for Carrying Out the Invention

[0017] <Battery Cell> Hereinafter, the battery cell 1 according to an embodiment of the present invention will be described. As shown in FIG. 1, the battery cell 1 according to the present embodiment includes a negative electrode layer 20, an electrolyte layer 4, and a positive electrode layer 30, which are laminated in this order. The battery cell 1 is, for example, a lithium ion battery cell using lithium ions as a charge transfer medium. The battery cell 1 may be a battery cell having a liquid electrolyte layer 4. On the other hand, since the configuration of the present embodiment shown below can preferably reduce the influence of dendrite precipitation, the battery cell 1 according to the present embodiment preferably has a solid electrolyte layer 4 that is easily affected by dendrite precipitation.

[0018] (Negative Electrode Layer) The negative electrode layer 20 is formed, for example, by forming a negative electrode active material layer 22 on a negative electrode current collector 21.

[0019] The negative electrode current collector 21 is not particularly limited, and any material known as a negative electrode current collector for a solid-state secondary battery can be used. Examples of negative electrode current collectors 21 include copper and stainless steel. The above-mentioned copper, stainless steel, etc., can be used, for example, in the form of foil.

[0020] The negative electrode active material layer 22 is a layer that essentially contains the negative electrode active material. In addition to the negative electrode active material, the negative electrode active material layer 22 may also contain a binder, a conductive additive, an electrolyte, etc. The binder, conductive additive, electrolyte, etc. are not particularly limited, and substances known as electrode materials for secondary batteries can be used.

[0021] The negative electrode active material is not particularly limited, and any material known as a negative electrode active material for secondary batteries can be used. On the other hand, the configuration of this embodiment shown below can preferably reduce the effect of dendrite deposition, which is particularly noticeable when lithium metal is used as the negative electrode active material. Therefore, it is preferable that the negative electrode active material layer 22 contains lithium metal as the negative electrode active material.

[0022] Examples of negative electrode active materials other than lithium metal include lithium titanate (Li4Ti5O4). 12 Examples include lithium transition metal oxides such as ), transition metal oxides such as TiO2, Nb2O3, and WO3, metal sulfides, metal nitrides, carbon materials such as graphite, soft carbon, and hard carbon, and metallic indium and lithium alloys.

[0023] As shown in Figures 1 and 2, the negative electrode active material layer 22 has a plurality of recesses 22a and a flat portion 22b on the surface facing the electrolyte layer 4.

[0024] As shown in Figures 1 and 2, the recess 22a is a cone-shaped recess having an inclined portion S. The formation of the recess 22a in the negative electrode active material layer 22 causes variations in current density, with the current density being higher near the recess 22a. As a result, dendrites are preferentially formed in the recess 22a, reducing the risk of dendrites piercing the electrolyte layer 4 and causing a short circuit. This improves the cycle characteristics of the battery cell 1. In addition to the above, the recess 22a can mitigate the non-uniformity of the pressure distribution caused by the expansion of the negative electrode layer 20 during charging of the battery cell 1. Furthermore, the recess 22a increases the contact area between the electrolyte layer 4 and the negative electrode active material layer 22, reducing resistance and improving the output of the battery cell 1.

[0025] Because the recess 22a is conical in shape with an inclined portion S, dendrites are more likely to be preferentially generated starting from the apex of the cone. In Figures 1 and 2, the shape of the recess 22a is shown as the recess of a square pyramid, but the shape of the recess 22a can be any conical shape, and it may be a polygonal pyramid other than a square pyramid, or it may be a cone.

[0026] The depth of the recess 22a is not particularly limited, and is limited to the thickness of the negative electrode active material layer 22.

[0027] Figure 2 shows the negative electrode active material layer 22 viewed from the electrolyte layer 4 side. In Figure 2, the recesses 22a have rectangular openings arranged regularly in rows, but the arrangement of the recesses 22a is not limited to this. The openings of the recesses 22a may be arranged regularly in an alternating pattern, or they may be arranged with a certain degree of irregularity. It is preferable that the recesses 22a are formed over the entire surface of the negative electrode active material layer 22 on the electrolyte layer 4 side.

[0028] The flat portion 22b is a surface substantially perpendicular to the stacking direction of the negative electrode active material layer 22. The flat portion 22b is a region on the electrolyte layer 4 side surface of the negative electrode active material layer 22 where recesses 22a are not formed. By having the flat portion 22b along with the recesses 22a, the negative electrode active material layer 22 can be constructed without forming protrusions on the electrolyte layer 4 side where the current density is high. Therefore, the formation of dendrites close to the electrolyte layer 4 can be suppressed. As shown in Figure 2, it is preferable that the flat portion 22b be positioned between each of the multiple recesses 22a. In other words, it is preferable that the openings of the multiple recesses 22a are not in close contact with each other.

[0029] (Positive electrode layer) The positive electrode layer 30 is formed, for example, by creating a positive electrode active material layer 31 on a positive electrode current collector 32.

[0030] The positive electrode active material layer 31 is a layer that essentially contains the positive electrode active material. In addition to the positive electrode active material, the positive electrode active material layer 31 may also contain a binder, a conductive additive, an electrolyte, etc. The binder, conductive additive, electrolyte, etc. are not particularly limited, and substances known as electrode materials for secondary batteries can be used.

[0031] The positive electrode active material is not particularly limited, and any known material used as a positive electrode active material for secondary batteries can be applied. Examples of positive electrode active materials include LiCoO2, LiNiO2, and LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 Layered cathode active material particles such as O2, LiVO2, LiCrO2, LiMn2O4, Li(Ni 0.25 Mn 0.75 )2O4, LiCoMnO4, Li2NiMn3O8, and other spinel-type cathode active materials, as well as olivine-type cathode active materials such as LiCoPO4, LiMnPO4, and LiFePO4 can be used.

[0032] The positive electrode current collector 32 is not particularly limited, and known materials for the positive electrode current collector of a secondary battery can be applied. Examples of the positive electrode current collector 32 include aluminum, stainless steel, etc. For the above aluminum, stainless steel, etc., those formed into a foil shape, for example, are used. In addition to the above, a conductive carbon sheet (for example, a graphite sheet or a CNT sheet) etc. may be used.

[0033] (Electrolyte layer) The electrolyte layer 4 may be a layer containing a solid electrolyte, or may be a layer containing an electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent. The electrolyte layer 4 is preferably a layer containing a solid electrolyte.

[0034] As the solid electrolyte contained in the electrolyte layer 4, known materials for the solid electrolyte used in a secondary battery can be applied. Examples of the solid electrolyte include sulfide-based solid electrolytes, oxide-based solid electrolytes, nitride-based solid electrolytes, halide-based solid electrolytes, etc.

[0035] As the electrolyte dissolved in the non-aqueous solvent contained in the electrolyte layer 4, known materials for the electrolyte used in a secondary battery can be applied.

[0036] Examples of the electrolyte dissolved in the non-aqueous solvent include LiPF6, LiBF4, LiClO4, LiN(SO2CF3), LiN(SO2C2F5)2, LiCF3SO3, LiC4F9SO3, LiC(SO2CF3)3, LiF, LiCl, LiI, Li2S, Li3N, Li3P, Li 10 GeP2S 12 (LGPS), Li3PS4, Li6PS5Cl, Li7P2S8I, Li x PO y N z (x = 2y + 3z - 5, LiPON), Li7La3Zr2O 12 (LLZO), Li 3x La 2 / 3-x TiO3(LLTO), Li 1+x Al x Ti 2-x (PO4)3(0 ≦ x ≦ 1, LATP), Li1.5 Al 0.5 Ge 1.5 (PO4)3(LAGP), Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 Li 1+x+y Al x (Ti,Ge) 2-x Si y P 3-y O 12 Li 4-2x Zn x Examples include GeO4 (LISICON). One of the above may be used alone, or two or more may be used in combination.

[0037] Examples of non-aqueous solvents for dissolving liquid electrolytes include aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones.

[0038] If the electrolyte layer 4 contains an electrolyte solution, the battery cell 1 may have a separator. The separator is located between the positive electrode layer and the negative electrode layer. Its material and thickness are not particularly limited, and known separators that can be used in secondary battery cells, such as polyethylene or polypropylene, can be applied.

[0039] <Method of manufacturing battery cells> The manufacturing method for the battery cell 1 according to the above embodiment can be manufactured using known secondary battery manufacturing methods, except for the method of forming a negative electrode active material layer 22 having recesses and flat portions on the surface of the electrolyte layer.

[0040] The negative electrode layer 20 and the positive electrode layer 30 may be formed by either a wet method or a dry method. For example, when forming the negative electrode layer 20 and the positive electrode layer 30 by a wet method, a method can be applied in which an electrode mixture slurry containing the electrode active material is coated onto the current collector using a known method such as the doctor blade method and then dried.

[0041] One method for forming the negative electrode active material layer 22 having recesses and flat surfaces is to press the negative electrode active material layer 22 on the negative electrode current collector 21 in the manufactured negative electrode layer 20 using a press device such as a uniaxial press or a roll press that has irregularities formed on its surface.

[0042] The electrolyte layer 4 can be formed by a process such as pressing the solid electrolyte if the electrolyte layer 4 is a solid electrolyte layer having a solid electrolyte. Alternatively, it may be formed by a process of applying a solid electrolyte paste, which is prepared by dispersing a solid electrolyte in a solvent, to the surface of a substrate or electrode.

[0043] A battery cell 1 is obtained by stacking the negative electrode layer 20, the electrolyte layer 4, and the positive electrode layer 30 in this order to form a laminate. This process may also involve pressing the laminate. Known means such as a roll press can be used for pressing.

[0044] Preferred embodiments of the present invention have been described above. The present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. [Examples]

[0045] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0046] [Battery cell fabrication] <Examples> After bonding lithium metal, which serves as the negative electrode active material, to copper foil, which serves as the negative electrode current collector, using a cladding material, a negative electrode active material layer was fabricated by pressing it using a uniaxial press with an uneven surface, resulting in a layer with regularly arranged square pyramidal recesses and flat surfaces as shown in Figure 2. Subsequently, a battery cell according to the embodiment was fabricated by laminating a solid electrolyte layer and a positive electrode layer, which were fabricated by conventional methods, with the fabricated negative electrode active material layer and performing an integrated pressing.

[0047] <Comparative Example> A comparative battery cell was fabricated in the same manner as in the examples, except that cone-shaped recesses were not formed on the surface of the negative electrode active material layer.

[0048] The initial charge-discharge efficiency (0.1c, 25°C) and initial DC resistance (DCR) (60°C) were measured using the battery cells of the above-described examples and comparative examples, but no significant differences were observed.

[0049] [Cycle characteristics test] Cycle performance tests (0.3c, 60°C) were performed using the battery cells of the above-described examples and comparative examples. Charge and discharge cycles were repeated 90 times for each of the battery cells of the examples and comparative examples, and the relationship between the number of cycles and discharge capacity (mAh) is shown in Figure 3. Note that the cycle performance test was performed with N=2 for the comparative example. As shown in Figure 3, the battery cells of the examples clearly show superior cycle performance compared to the battery cells of the comparative examples, as the discharge capacity does not decrease easily even when the number of cycles is increased. [Explanation of Symbols]

[0050] 1 battery cell 20 Negative electrode layer 22 Negative electrode active material layer 22a Recess 22b Plane part 30 Positive electrode layer 4 Electrolyte layer S slope part

Claims

1. A battery cell having a negative electrode layer, an electrolyte layer, and a positive electrode layer, The negative electrode active material layer in the negative electrode layer has recesses and flat surfaces on the surface facing the electrolyte layer. The recess is a conical recess having an inclined portion, The aforementioned electrolyte layer is a solid electrolyte layer containing a solid electrolyte, in this battery cell.

2. The battery cell according to claim 1, wherein the negative electrode active material layer contains lithium metal.

3. The battery cell according to claim 1 or 2, wherein a plurality of recesses are formed, and the planar portions are each formed between the plurality of recesses.

Images