Battery

Abstract

To provide a battery that has improved safety necessary when the battery goes into a short-circuit state.SOLUTION: A battery is provided, comprising a cell in which a negative electrode collector, a negative-electrode active material layer, an electrolyte layer, a positive-electrode active material and a positive electrode collector are provided in this order. The negative-electrode active material layer contains lithium titanate. The positive electrode collector has such a fusing characteristics that the positive electrode collector is more liable to fuse than the negative electrode collector.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Batteries having cells each having an anode current collector, an anode active material layer, an electrolyte layer, a cathode active material layer, and a cathode current collector in this order are known. In addition, a technology for improving safety in batteries during short circuits is known. For example, Patent Document 1 discloses a battery characterized in that, when a short circuit is formed between two batteries, the first current collector and the second current collector are formed with a thickness such that the short circuit is interrupted by melting the short circuit at the short-circuited portion of the first current collector and the second current collector before the temperature of the battery reaches a predetermined value due to heat generated by the current flowing through the short circuit. In addition, for example, Patent Document 2 discloses providing a high heat capacity member on the current collector. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-064767 A [Patent Document 2] JP 2016-207614 A Summary of the Invention [Problem to be solved by the invention]

[0004] It is preferable to further improve the safety of a battery in the event of a short circuit (internal short circuit). In Patent Document 1, when a short circuit occurs, the short-circuited portion of the current collector is melted to cut off the short circuit, thereby suppressing an increase in battery temperature. On the other hand, if the short-circuited portion of the current collector melts immediately after the occurrence of a short circuit, a new problem arises in that the battery may be maintained at a high SOC (state of charge).

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and has as its main object to provide a battery with improved safety in the event of a short circuit. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides a battery including a cell having a negative electrode current collector, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector in this order, wherein the negative electrode active material layer contains lithium titanate, and the positive electrode current collector has a fusing characteristic that makes it more likely to fusing than the negative electrode current collector.

[0007] According to the present disclosure, the negative electrode active material layer contains lithium titanate, and the positive electrode current collector has fusing characteristics that make it more likely to fuse than the negative electrode current collector, resulting in a battery with improved safety in the event of a short circuit. Effect of the Invention

[0008] The present disclosure has an effect of providing a battery with improved safety in the event of a short circuit. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. [Diagram 2] 1 is a graph showing the results of a nail penetration test in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The battery according to the present disclosure will be described in detail below.

[0011] FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. The battery 20 shown in FIG. 1 is a stacked battery in which two cells 10 (10A, 10B) are stacked. The cell 10A has an anode current collector 1, an anode active material layer 2a, an electrolyte layer 3a, a cathode active material layer 4a, and a cathode current collector 5a, in this order. On the other hand, the cell 10B has an anode current collector 1, an anode active material layer 2b, an electrolyte layer 3b, a cathode active material layer 4b, and a cathode current collector 5b, in this order. The cells 10A and 10B share one anode current collector 1, and are connected in parallel. The anode active material layers (2a, 2b) contain lithium titanate. The cathode current collectors (5a, 5b) have a fusing characteristic that makes them more likely to fusing than the anode current collector 1.

[0012] According to the present disclosure, the negative electrode active material layer contains lithium titanate, and the positive electrode current collector has a fusing characteristic that makes it easier to fuse than the negative electrode current collector, resulting in a battery with improved safety in the event of a short circuit. Here, "the positive electrode current collector has a fusing characteristic that makes it easier to fuse than the negative electrode current collector" means that in the event of a battery short circuit (internal short circuit), the positive electrode current collector fuses before the negative electrode current collector.

[0013] In the above-mentioned Patent Document 1, when a short circuit occurs, the short-circuited portion of the current collector is melted to cut off the short circuit, thereby suppressing an increase in the battery temperature. However, if both the positive electrode current collector and the negative electrode current collector melt immediately after the short circuit occurs, discharge may not proceed thereafter, and the battery may remain at a high SOC.

[0014] In contrast, in the present disclosure, the positive electrode current collector has a fusing characteristic that makes it easier to fuse than the negative electrode current collector. Therefore, the positive electrode current collector fuses immediately after the occurrence of a short circuit, and the short circuit between the positive electrode current collector and the negative electrode current collector is immediately cut off. Meanwhile, the short circuit between the positive electrode active material layer and the negative electrode current collector continues. As a result, the discharge continues even after the occurrence of a short circuit, and the SOC of the battery can be reduced. Here, the short circuit resistance between the current collectors is smaller than the short circuit resistance between the active material layer and the current collector, and the short circuit current is larger. Therefore, the amount of heat generated by the short circuit (Joule heat=I 2R) is larger in the case of a short circuit between the current collectors. Therefore, immediately interrupting the short circuit between the current collectors is more effective in suppressing the rise in the battery temperature. In addition, the negative electrode active material layer in the present disclosure contains lithium titanate. Lithium titanate has a property of undergoing a phase transition to a low electronic conductor close to insulation upon discharge. Therefore, when a short circuit continues between the positive electrode active material layer and the negative electrode current collector, the negative electrode active material layer becomes highly resistive upon discharge. When the negative electrode active material layer becomes highly resistive, the short circuit current decreases, so that the amount of heat generated can be reduced. In this way, the battery in the present disclosure can continue discharging (reducing SOC) even after a short circuit while suppressing a rise in temperature, thereby improving safety during a short circuit.

[0015] In addition, since the positive electrode active material layer may be thermally decomposed and release oxygen as the temperature rises, it is preferable to preferentially suppress the temperature rise of the positive electrode active material layer. For example, if the negative electrode collector has a fusing characteristic that is easier to melt than the positive electrode collector, the short circuit between the negative electrode active material layer and the positive electrode collector may continue, making it difficult to preferentially suppress the temperature rise of the positive electrode active material layer. In contrast, in the present disclosure, since the positive electrode collector has a fusing characteristic that is easier to melt than the negative electrode collector, there is also an advantage that the release of oxygen from the positive electrode active material layer can be suppressed. In addition, the above-mentioned Patent Document 2 discloses that a high heat capacity member is provided on the current collector. By providing a high heat capacity member, the heat capacity per unit capacity of the battery can be increased, and the temperature rise during a short circuit can be suppressed. On the other hand, since a new high heat capacity member is provided, the energy density of the battery is reduced. In contrast, in the present disclosure, the temperature rise of the battery can be suppressed without providing a high heat capacity member, so there is an advantage in terms of energy density.

[0016] 1. Cell The cell in the present disclosure includes, in this order, a negative electrode current collector, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector. In the cell in the present disclosure, the negative electrode active material layer contains lithium titanate. Details of each member will be described later.

[0017] In the present disclosure, the positive electrode current collector has a fusing characteristic that makes it easier to fuse than the negative electrode current collector. Such fusing characteristic can be adjusted, for example, by changing at least one of the thickness and the melting point of the current collector.

[0018] In the present disclosure, it is preferable to satisfy any one of the following conditions (i) to (iii). Condition (i): The thickness T1 of the negative electrode current collector is the same as the thickness T2 of the positive electrode current collector, and the melting point M1 of the negative electrode current collector is higher than the melting point M2 of the positive electrode current collector. Condition (ii): The melting point M1 of the negative electrode current collector is the same as the melting point M2 of the positive electrode current collector, and the thickness T1 of the negative electrode current collector is greater than the thickness T2 of the positive electrode current collector. Condition (iii): The thickness T1 of the negative electrode current collector is greater than the thickness T2 of the positive electrode current collector, and the melting point M1 of the negative electrode current collector is higher than the melting point M2 of the positive electrode current collector.

[0019] Here, "the thickness T1 of the negative electrode current collector is the same as the thickness T2 of the positive electrode current collector" means that T2 relative to T1 (T2 / T1) is 0.99 or more and 1.01 or less. Also, "the melting point M1 of the negative electrode current collector is the same as the melting point M2 of the positive electrode current collector" means that M2 relative to M1 (M2 / M1) is 0.99 or more and 1.01 or less.

[0020] When the thickness T1 of the negative electrode current collector is thicker than the thickness T2 of the positive electrode current collector, T2 / T1 is, for example, 0.40 or more, and may be 0.50 or more, while T2 / T1 is, for example, 0.95 or less, may be 0.80 or less, may be 0.70 or less, or may be 0.60 or less.

[0021] When the thickness T1 of the negative electrode current collector is thicker than the thickness T2 of the positive electrode current collector, T1-T2 is, for example, 1 μm or more, or may be 5 μm or more, 10 μm or more, or may be 20 μm or more, whereas T1-T2 is, for example, 100 μm or less, or may be 50 μm or less.

[0022] When the melting point M1 of the negative electrode current collector is higher than the melting point M2 of the positive electrode current collector, M2 / M1 is, for example, 0.10 or more, or may be 0.30 or more, or may be 0.50 or more, whereas M2 / M1 is, for example, 0.95 or less, or may be 0.70 or less.

[0023] When the melting point M1 of the negative electrode current collector is higher than the melting point M2 of the positive electrode current collector, M1-M2 is, for example, 10° C. or higher, and may be 50° C. or higher, 100° C. or higher, or 300° C. or higher. On the other hand, M1-M2 is, for example, 3000° C. or lower, and may be 2000° C. or lower, 1000° C. or lower, or 500° C. or lower.

[0024] (1) Negative electrode active material layer The negative electrode active material layer contains lithium titanate. Lithium titanate usually functions as a negative electrode active material. The negative electrode active material layer may contain at least one of an electrolyte, a conductive material, and a binder, as necessary.

[0025] Lithium titanate is a compound containing at least Li, Ti and O. At least one of the Li and Ti elements may be partially substituted with another element. Examples of lithium titanate include Li 2 TiO 3 , Li 4 Ti 5 O 12 and Li 2 Ti 2 O 5 Among these, Li 4 Ti 5 O 12 The negative electrode active material layer may contain only one type of lithium titanate, or may contain two or more types of lithium titanate.

[0026] The shape of lithium titanate may be, for example, particulate. The particle diameter (D 50 ) is, for example, 0.5 μm or more and 5 μm or less.

[0027] The proportion of lithium titanate in the negative electrode active material layer is, for example, 40% by weight or more, or may be 50% by weight or more, or may be 60% by weight or more, while the proportion of lithium titanate in the negative electrode active material layer is, for example, 80% by weight or less.

[0028] Examples of the conductive material include carbon materials such as acetylene black (AB), ketjen black (KB), carbon fiber, carbon nanotube (CNT), and carbon nanofiber (CNF). Examples of the binder include rubber-based binders such as butylene rubber (BR) and styrene butadiene rubber (SBR), and fluoride-based binders such as polyvinylidene fluoride (PVDF). Examples of the electrolyte include the same materials as those described in "(4) Electrolyte Layer".

[0029] The thickness of the negative electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

[0030] (2) Negative electrode current collector and positive electrode current collector The material and thickness of the negative electrode current collector and the positive electrode current collector preferably satisfy any one of the above-mentioned conditions (i) to (iii). Examples of the material of the negative electrode current collector include SUS, copper, nickel, and carbon. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. The thickness of the negative electrode current collector and the positive electrode current collector is, for example, 1 μm or more and 1 mm or less. Examples of the shape of the negative electrode current collector and the positive electrode current collector include a foil shape, a mesh shape, and a porous shape.

[0031] (3) Positive electrode active material layer The positive electrode active material layer contains at least a positive electrode active material, and may contain at least one of an electrolyte, a conductive material, and a binder, as necessary. The electrolyte, the conductive material, and the binder are the same as those described in "(1) Negative electrode active material layer."

[0032] The positive electrode active material is not particularly limited, but may be, for example, an oxide active material. Examples of the oxide active material include LiCoO 2 , LiMnO 2 , LiNiO 2 , LiVO 2 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 Rock salt layered active materials such as LiMn 2 O 4 , Li 4 Ti 5 O 12 , Li(Ni 0.5 Mn 1.5 )O 4 Spinel-type active materials such as LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 Examples of the olivine type active material include those mentioned above.

[0033] The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

[0034] (4) Electrolyte layer The electrolyte layer contains at least an electrolyte, and may contain a binder as necessary. The binder is the same as that described in "(1) Negative electrode active material layer."

[0035] The electrolyte may be a solid electrolyte or a liquid electrolyte. Examples of the solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes.

[0036] The thickness of the electrolyte layer is, for example, not less than 0.1 μm and not more than 1000 μm.

[0037] 2.Battery The battery in the present disclosure includes the above-mentioned cells. The number of cells included in the battery may be one or may be two or more. In the latter case, the number of cells is, for example, two or more and 200 or less. When the number of cells is two or more, the cells may be connected in series or in parallel.

[0038] The type of the battery in the present disclosure is not particularly limited, but is typically a lithium ion secondary battery. In addition, the battery in the present disclosure may be a solid-state battery (all-solid-state battery) using a solid electrolyte as the electrolyte, or a liquid-based battery using a liquid electrolyte (electrolytic solution) as the electrolyte.

[0039] Examples of applications of the battery in the present disclosure include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered automobiles, diesel-powered automobiles, etc. The battery in the present disclosure may also be used as a power source for moving objects other than vehicles (e.g., railways, ships, and aircraft), and may also be used as a power source for electrical appliances such as information processing devices.

[0040] The present disclosure is not limited to the above-described embodiment. The above-described embodiment is merely an example, and any configuration that is substantially the same as the technical idea described in the claims of the present disclosure and that exhibits similar effects is included in the technical scope of the present disclosure. EXAMPLES

[0041] [Example 1] An all-solid-state battery (battery for evaluation) was fabricated that had a plurality of cells in the thickness direction, each having a negative electrode current collector, a negative electrode active material layer, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector in this order. 4 Ti 5 O 12 ), binder (PVdF-based binder), and sulfide solid electrolyte (LiBr, LiI-containing Li 2 SP 2 S 5The layer used was a layer containing a cathode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 ), binder (PVdF-based binder), and sulfide solid electrolyte (LiBr, LiI-containing Li 2 SP 2 S 5 The layer used was made of a material containing a binder (butadiene rubber) and a sulfide solid electrolyte (LiBr, LiI-containing LiI). 2 SP 2 S 5 A layer containing a Cr-based glass ceramic was used. Ni foil (melting point: 1455°C, thickness: 15 μm) was used as the negative electrode current collector, and Al foil (melting point: 660°C, thickness: 15 μm) was used as the positive electrode current collector.

[0042] [Example 2] A battery for evaluation was produced in the same manner as in Example 1, except that Ni foil (melting point: 1455° C., thickness: 22 μm) was used as the negative electrode current collector.

[0043] [Reference example 1] A battery having a high heat capacity member (copper foil) was fabricated by referring to the examples of the above-mentioned Patent Document 2 (JP 2016-207614 A).

[0044] [evaluation] (Nail penetration test) A nail penetration test was performed on the battery obtained in Example 1. The change in the temperature of the battery during the nail penetration test was measured. In addition, the voltage value and the current value were obtained to measure the change in the state of charge (SOC) of the battery. The results are shown in FIG. 2. As shown in FIG. 2, when a nail penetration test was performed on a battery equipped with a plurality of positive electrode collectors and negative electrode collectors, three peaks of short circuit current due to short circuit between the collectors were confirmed. Since the peak shape was sharp, it was found that the short circuit path between the collectors was cut off immediately after the short circuit occurred. This is considered to be because the positive electrode collector melted immediately after the short circuit occurred. In addition, a small amount of short circuit current was confirmed between each peak, and it was confirmed that the SOC decreased even after the short circuit occurred. This is considered to be because the short circuit between the positive electrode active material layer and the negative electrode collector was maintained and discharge proceeded even after the short circuit occurred. In addition, the battery temperature peaked at the third short circuit between the collectors (dotted line in the figure) and then decreased. This is considered to be because the resistance of the negative electrode active material containing lithium titanate increased due to discharge.

[0045] (energy density) The energy density was evaluated for the batteries obtained in Examples 1 and 2 and Reference Example 1. The results are shown in Table 1.

[0046] [Table 1]

[0047] As shown in Table 1, in Example 2, the thickness per cell increased by 7 μm compared to Example 1, and therefore the energy density per cell decreased by 3.59%. In Reference Example 1, the thickness per cell increased by 60 μm compared to Example 1, and therefore the energy density per cell decreased by 25.7%. In addition, the layer structure of the battery in Example 2 was similar to that of the battery in Example 1, and therefore the amount of heat generated was small. On the other hand, the layer structure of the battery in Reference Example 1 was different from that of the battery in Example 1, and therefore the amount of heat generated was large. [Explanation of symbols]

[0048] 1...Negative electrode current collector 2...Negative electrode active material layer 3...electrolyte layer 4...Cathode active material layer 5...Positive electrode current collector 10…Cell 20...battery

Claims

[Claim 1] A negative electrode current collector, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector, in this order. A battery comprising a cell comprising: The negative electrode active material layer contains only lithium titanate as a negative electrode active material, the positive electrode current collector has a fusing characteristic that makes it easier to fuse than the negative electrode current collector, The negative electrode current collector is a Ni foil, The positive electrode current collector is an Al foil, When the thickness of the negative electrode current collector is T1 and the thickness of the positive electrode current collector is T2, the thickness of T1 is greater than the thickness of T2, and T1-T2 is 5 μm or more and 10 μm or less, The electrolyte layer contains a sulfide solid electrolyte as an electrolyte, The battery, wherein the positive electrode active material layer contains LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 as a positive electrode active material.

Images