Testing methods for secondary batteries, secondary batteries

Abstract

In secondary batteries, this method efficiently performs short-circuit testing at locations with a high probability of short circuits. [Solution] The method includes the steps of: measuring a first surface temperature, which is the temperature of the end face of the electrode stack; connecting charge / discharge probes to the positive and negative terminals of the electrode stack and applying a current; measuring a second surface temperature, which is the temperature of the end face of the electrode stack when the current is applied; and determining whether or not a short circuit has occurred based on the difference between the first surface temperature and the second surface temperature.

Description

[Technical Field]

[0001] This disclosure relates to a method for inspecting secondary batteries. [Background technology]

[0002] When an internal short circuit occurs in a secondary battery, a large current flows, generating gas and heat, causing a rapid temperature rise. Patent Document 1 discloses a method for detecting changes in internal temperature and comparing the rate of change with a reference value to determine if an internal short circuit has occurred. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2002-008631 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Conventional techniques require detecting temperature changes inside the electrode body, which makes the inspection time-consuming. Furthermore, it was impossible to determine whether a short circuit was occurring inside the electrode body or on its surface.

[0005] Therefore, this disclosure aims to efficiently perform short-circuit testing in secondary batteries at locations with a high probability of short circuits. [Means for solving the problem]

[0006] This application discloses a method for inspecting a short circuit in a secondary battery, comprising the steps of: measuring a first surface temperature, which is the temperature of the end face of the electrode stack; connecting charge / discharge probes to the positive and negative terminals of the electrode stack and applying a current; measuring a second surface temperature, which is the temperature of the end face of the electrode stack when the current is applied; and determining whether or not a short circuit exists based on the difference between the first surface temperature and the second surface temperature.

[0007] The measurement of the first surface temperature and the second surface temperature may be performed using a thermographic device.

[0008] The electrode laminate may have a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer.

[0009] Furthermore, this application discloses a secondary battery in which, after inspection using the above-described method for inspecting a short circuit in a secondary battery, probe marks from a charge / discharge probe are formed on the positive electrode terminal connected to the positive electrode current collector layer and the negative electrode terminal connected to the negative electrode current collector layer. [Effects of the Invention]

[0010] By inspecting the surface temperature of the end face (cut surface) of electrode stacks, where short circuits are likely to occur during the manufacturing process, short circuit detection can be efficiently performed at locations with a high probability of short circuits. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 illustrates the layer structure of the solid-state battery 10. [Figure 2] Figure 2 illustrates a scene from the short-circuit inspection method S10 for secondary batteries. [Figure 3] Figure 3 illustrates another scenario of the short-circuit inspection method S10 for secondary batteries. [Modes for carrying out the invention]

[0012] 1. Battery configuration First, a configuration example of a secondary battery to be inspected will be described. FIG. 1 shows a diagram for explaining a solid battery (all-solid-state battery) according to one form. Here, although it will be described by taking an all-solid-state battery as one typical example, the present disclosure does not necessarily have to be an all-solid-state battery, and it is applicable to any battery having an electrode body and an exterior body for sealing the same (for example, a solid battery (semi-solid-state battery) including a solid electrolyte and an electrolytic solution, or a battery using only all electrolytic solutions). FIG. 1 shows the layer configuration of an electrode laminate 11 included therein among solid batteries. A solid battery is formed by sealing such an electrode laminate 11 in an exterior body. For example, an electrode laminate 11 that is generally rectangular in plan view is included in an exterior body that is generally rectangular in plan view. At this time, a positive electrode terminal extends from the positive electrode current collector of the electrode laminate 11, and a negative electrode terminal extends from the negative electrode current collector, and their tips are arranged so as to protrude from the exterior body. Each configuration of the electrode laminate 11 and their relationships will be described in more detail below.

[0013] The electrode laminate 11 has a positive electrode current collector 12, a positive electrode composite layer 13, an electrolyte layer 14, a negative electrode composite layer 15, and a negative electrode current collector 16. In this form, the positive electrode current collector 12, the positive electrode composite layer 13, the electrolyte layer 14, the negative electrode composite layer 15, and the negative electrode current collector 16 are laminated in this order to form a unit element 11a, and a plurality of these unit elements 11a are laminated to form an electrode body 11 (only one unit element 11a is shown in FIG. 1). And 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.

[0014] 1.1. Positive electrode current collector The positive electrode current collector 12 is laminated on the positive electrode composite layer 13 to collect current from the positive electrode composite layer 13. In this form, the positive electrode current collector 12 is in the shape of a square foil in plan view, and can be composed of a positive electrode current collecting foil that is a metal foil, and a conductive resin layer or a carbon layer laminated on the positive electrode current collecting foil. The positive electrode current collector 12 is laminated on the positive electrode composite layer 13 by laminating a carbon layer on the positive electrode composite layer 13. Examples of the material constituting the positive electrode current collector include materials of metal foils such as stainless steel, nickel, chromium, gold, platinum, aluminum, iron, titanium, and zinc. Those obtained by plating or vapor-depositing nickel, chromium, carbon, etc. on these metal foils may also be used. The conductive resin layer can be composed of a resin in which a conductive material is dispersed, and the carbon layer can be composed of a material containing carbon.

[0015] 1.2. Positive electrode composite layer On one surface of the positive electrode composite layer 13, the above-described positive electrode current collector 12 is laminated, and on the other surface, the electrolyte layer 14 is laminated. In this embodiment, the positive electrode composite layer 13 is in the form of a square sheet in plan view. The positive electrode composite layer 13 is a layer containing at least a positive electrode active material. Further, the positive electrode composite layer may contain at least one of an electrolyte, a conductive auxiliary material, and a binder, if necessary. [[ID= 7]] The thickness of the positive electrode composite layer 13 is not particularly limited, but can be 1 μm or more and 100 μm or less, and more preferably 30 μm or more and 100 μm or less.

[0016] [Positive electrode active material] Examples of the positive electrode active material include oxide active materials. Examples of the oxide active material include ternary systems (Li(Ni x Co y Mn z )O2), NCA systems (Li(Ni x Co y Al z )O2), LiCoO2, LiMnO2, LiNiO2, LiVO2, Li 1+x Ni [[ID= 29]] 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and other rock salt layer-type active materials, LiMn2O4, Li4Ti5O 12 , Li(Ni 0.5 Mn 1.5 )O4 and other spinel-type active materials, LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4 and other olivine-type active materials, Li 1+x Mn 2-x-y M yHeteroatomic substitution Li-Mn spinel active material represented as O4 (where M is one or more selected from Al, Mg, Co, Fe, Ni, Zn), Li x TiO y One could list these:

[0017] A coating layer containing a Li-ion conductive oxide may be formed on the surface of the active material. This is because it can suppress the reaction between the active material and the solid electrolyte (especially sulfide solid electrolytes). Examples of Li-ion conductive oxides include LiNbO3 and Li4Ti5O. 12 Li3PO4 is an example. The thickness of the coating layer is, for example, between 1 nm and 30 nm.

[0018] The positive electrode active material can take the form of particulate matter, for example. The average particle size (D50) of the positive electrode active material is not particularly limited, but may be, for example, 10 nm or more, or 100 nm or more. On the other hand, the average particle size (D50) of the positive electrode active material may be, for example, 50 μm or less, or 20 μm or less. The average particle size (D50) can be calculated, for example, from measurements using a laser diffraction particle size analyzer or a scanning electron microscope (SEM).

[0019] [Electrolyte] In all-solid-state batteries and semi-solid-state batteries, the electrolyte includes at least a solid electrolyte, but in semi-solid-state batteries and batteries using only an electrolyte, it includes a liquid electrolyte (electrolyte).

[0020] Examples of solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes, and organic polymer electrolytes such as polymer electrolytes. Examples of sulfide solid electrolytes include solid electrolytes containing Li, X (where X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. Furthermore, sulfide solid electrolytes may further contain at least one of O and halogen elements. Examples of halogen elements include F, Cl, Br, and I. Sulfide solid electrolytes may be glass (amorphous) or glass ceramics. Examples of sulfide solid electrolytes include Li2S-P2S5, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-GeS2, and Li2S-P2S5-GeS2.

[0021] The electrolyte preferably contains a supporting salt and a solvent. Examples of supporting salts (lithium salts) for lithium-ion conductive electrolytes 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. Examples of solvents used in the electrolyte include cyclic esters (cyclic carbonates) such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), and linear esters (linear carbonates) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The electrolyte preferably contains two or more solvents.

[0022] The mass ratio of the positive electrode active material to the electrolyte is preferably 85 / 15 to 30 / 70, and more preferably 80 / 20 to 50 / 50, in terms of positive electrode active material / electrolyte.

[0023] [Conductive additives / binders] Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and Ketjenblack (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs). Examples of binders include rubber-based binders and fluoride-based binders.

[0024] 1.3. Electrolyte layer The electrolyte layer 14 is a layer formed between the positive electrode composite layer and the negative electrode composite layer, and contains at least an electrolyte. The electrolyte may consist only of a solid electrolyte, or it may also contain a liquid electrolyte (electrolyte). The specific solid electrolyte and electrolyte are the same as those described for the positive electrode composite layer above. The thickness of the electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less. More preferably, it is 0.1 μm or more and 300 μm or less, and even more preferably 1 μm or more and 100 μm or less.

[0025] 1.4.Negative electrode composite layer The negative electrode composite layer 15 is a layer containing at least a negative electrode active material and may contain at least one of an electrolyte, a conductive additive, and a binder. The electrolyte, conductive additive, and binder are the same as those described above for the positive electrode composite layer. The thickness of the negative electrode composite layer 15 is not particularly limited, but can be 1 μm or more and 100 μm or less, and more preferably 30 μm or more and 100 μm or less.

[0026] [Negative electrode active material] The negative electrode active material is a material that expands during charging. While not specifically limited, examples include graphite, silicon, metallic lithium, and lithium titaniobate.

[0027] 1.5. Negative electrode current collector The negative electrode current collector 16 is laminated on the negative electrode composite layer 15 and collects current from the negative electrode composite layer 15. In this embodiment, the negative electrode current collector 16 is a rectangular foil in plan view and can be made of, for example, stainless steel, copper, nickel, carbon, and aluminum, or alloys thereof. Alternatively, these materials may be plated or vapor-deposited with nickel, chromium, or carbon.

[0028] 1.6. Positive terminal, negative terminal The positive and negative terminals are conductive materials and serve as terminals for electrically connecting each pole to the outside. One end of the positive terminal is electrically connected to the positive current collector 12, and the other end penetrates the outer casing and is exposed to the outside. One end of the negative terminal is electrically connected to the negative current collector 16, and the other end penetrates the outer casing and is exposed to the outside. Furthermore, since charge / discharge probes are connected to the positive and negative terminals in the short-circuit testing method for secondary batteries described later, probe marks are formed there. These probe marks deform the surfaces of the positive and negative terminals, increasing their surface area and thus improving heat dissipation performance.

[0029] 1.7. Exterior The outer casing consists of rectangular sheet-like members in plan view, and includes, for example, a first sheet and a second sheet. The electrode body 11 is enclosed between the first sheet and the second sheet, and the outer edges of the first sheet and the outer edges of the second sheet are joined and sealed. Therefore, this outer casing is bag-shaped, and it encloses and seals the electrode body 11 inside.

[0030] The first and second sheets can be made of laminate film. Here, 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, or polyvinyl chloride.

[0031] 1.8. Others The laminated electrode body 11 is formed by creating a large laminate and then cutting it. As a result, in the rectangular parallelepiped shown in Figure 1, the end faces of each layer appear on four sides, which are the cut surfaces formed by the cutting process. The positive electrode terminal and the negative electrode terminal are provided on one pair of cut surfaces (shown as A in Figure 1) that are located on opposite sides of the four cut surfaces. The cut surface where neither the positive nor negative electrode terminal is located is denoted as B. Therefore, in this embodiment, cut surface B is the pair of cut surfaces located on opposite sides of the same cut surface.

[0032] 2. Method for testing short circuits in secondary batteries Next, a short-circuit inspection method S10 for a secondary battery according to one embodiment example (hereinafter sometimes referred to as "short-circuit inspection method S10") will be described. The short-circuit inspection method S10 of this embodiment example comprises the processes of first surface temperature measurement S11, current application S12, second surface temperature measurement S13, difference calculation S14, and short-circuit determination S15. The following describes each step.

[0033] 2.1. First surface temperature measurement In the first surface temperature measurement S11, the temperature of the secondary battery is measured before the next current application S12. A schematic diagram is shown in Figure 2, which shows the secondary battery in a plan view, with the four sides of the rectangle being the cross-sections. For clarity, Figure 2 shows the electrode stack 11, but in reality, this is covered by an outer casing. The surface temperature measured here is that of the outer casing in contact with the cut surface B. In other words, it is the cut surface, the surface where no electrode terminals are located. In this configuration, measurements are performed using a thermographic device. A thermographic device allows for non-contact image inspection, enabling accurate and efficient inspection by allowing for a comprehensive understanding of the temperature state of the target surface. However, other temperature measurement devices may be used in conjunction with or in addition to the thermographic device.

[0034] 2.2. Current Application In current application S12, charge / discharge probes are connected to the positive and negative terminals to apply current. A schematic diagram is shown in Figure 3. The magnitude of the applied current is not particularly limited, but it is generally between 2A and 30A. Similarly, the application time is not particularly limited, but 1 to 2 seconds is sufficient. Furthermore, this charge / discharge probe leaves contact marks on the positive and negative terminals, which contribute to heat dissipation as described above.

[0035] 2.3.Second surface temperature measurement In the second surface temperature measurement S13, the temperature of the secondary battery is measured after the current is applied S12. Preferably, the temperature measurement location and method are the same as in the first surface temperature measurement S11.

[0036] 2.4. Difference operation In the difference calculation S14, the difference between the temperatures measured in the first surface temperature measurement S11 and the second surface temperature measurement S13 is taken. If a thermographic device or temperature measurements are taken at multiple points, for example, the difference between the temperature of the highest temperature point among the measured areas is taken. In addition, it is also possible to measure many small sections of the inspection surface and compare the highest temperatures of the same inspection surface. This allows for obtaining differences at approximately the same location. In other words, when the temperature obtained by the first surface temperature measurement S11 is T1 and the temperature obtained by the second surface temperature measurement S13 is T2, the difference is taken using the formula ΔT = T2 - T1. Since current is applied S12 and energy is flowing, ΔT > 0 is usually the case regardless of whether there is a short circuit or not.

[0037] 2.5. Short-circuit detection In the short-circuit detection step S15, a determination is made as to whether a short circuit has occurred based on the value of ΔT obtained in the difference calculation S14. This determination can be made by setting a threshold value based on the magnitude of ΔT. The magnitude of the threshold value will vary depending on the type of battery, etc., so it is advisable to obtain it in advance through experiments, etc., and create a map or database based on it. Normally, a short circuit can be detected when ΔT exceeds a threshold. While there are no specific limitations on the threshold, it can be set to, for example, around 5°C.

[0038] 3. Effects, etc. This method for testing secondary batteries for short circuits allows for efficient short-circuit testing at locations with a high probability of short circuits by inspecting the surface temperature of the end face (cut surface) of the electrode stack, where short circuits are likely to occur during the manufacturing process. Furthermore, it is possible to understand not only short circuits but also the temperature behavior of the battery during initial charging. [Explanation of Symbols]

[0039] 11…Electrode laminate, 12…Positive electrode current collector, 13…Positive electrode composite layer, 14…Solid electrolyte layer, 15…Negative electrode composite layer, 16…Negative electrode current collector

Claims

1. A step of measuring the first surface temperature, which is the temperature of the end face of the electrode stack, The process involves connecting charge / discharge probes to the positive and negative terminals of the electrode stack and applying current, A step of measuring the second surface temperature, which is the temperature of the end face of the electrode stack when the current is applied, The process includes a step of determining whether or not a short circuit is present based on the difference between the first surface temperature and the second surface temperature. A method for testing short circuits in secondary batteries.

2. The method for inspecting a short circuit in a secondary battery according to claim 1, wherein the measurement of the first surface temperature and the measurement of the second surface temperature are performed using a thermographic device.

3. The method for testing a short circuit in a secondary battery according to claim 1 or 2, wherein the electrode stack comprises a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer.

4. A secondary battery, wherein a short-circuit inspection method for a secondary battery described in claim 3 is performed, and probe marks of the charge / discharge probe are formed on the positive electrode terminal connected to the positive electrode current collector layer and the negative electrode terminal connected to the negative electrode current collector layer.

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