JP7652064B2 - battery - Google Patents

Description

This disclosure relates to batteries.

Batteries having cells each having a negative electrode collector, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode collector in this order are known. Technologies for improving safety in batteries in the event of a short circuit are also known. For example, Patent Document 1 discloses a battery characterized in that, when a short circuit is formed between two batteries, the first and second current collectors are formed to such a thickness that the short circuit is interrupted by melting the short-circuited portions of the first and second current collectors before the temperature of the batteries reaches a predetermined value due to heat generated by the current flowing through the short circuit. Also, for example, Patent Document 2 discloses providing a high heat capacity member on the current collector.

JP 2009-064767 A JP 2016-207614 A

It is preferable to further improve the safety of the 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 interrupt the short circuit, thereby suppressing the rise in battery temperature. On the other hand, if the short-circuited portion of the current collector melts immediately after the short circuit occurs, a new problem arises in that the battery may be maintained at a high SOC (state of charge).

This disclosure was made in consideration of the above-mentioned circumstances, and its main objective is to provide a battery with improved safety in the event of a short circuit.

To solve the above problem, a battery is provided that includes 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, in which 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.

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 easier to fuse than the negative electrode current collector, resulting in a battery with improved safety in the event of a short circuit.

The present disclosure has the effect of providing a battery with improved safety in the event of a short circuit.

FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. 1 is a graph showing the results of a nail penetration test in Example 1.

The batteries in this disclosure are described in detail below.

1 is a schematic cross-sectional view illustrating a battery in 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. In addition, the cathode current collectors (5a, 5b) have a fusing characteristic that makes them more likely to melt than the anode current collector 1.

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 melt 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 melt than the negative electrode current collector" means that in the event of a battery short circuit (internal short circuit), the positive electrode current collector melts before the negative electrode current collector.

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 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.

In contrast, in the present disclosure, the positive electrode collector has a fusing characteristic that is easier to fuse than the negative electrode collector. Therefore, the positive electrode collector fuses immediately after the short circuit occurs, and the short circuit between the positive electrode collector and the negative electrode collector is immediately cut off. On the other hand, the short circuit between the positive electrode active material layer and the negative electrode collector continues. As a result, the discharge continues even after the short circuit occurs, and the SOC of the battery can be reduced. Here, the short circuit resistance between the collectors is smaller than the short circuit resistance between the active material layer and the collector, and the short circuit current is large. Therefore, the amount of heat generated by the short circuit (Joule heat = I ² R) is larger in the case of a short circuit between the collectors. Therefore, immediately cutting off the short circuit between the 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 resistant due to discharge. When the negative electrode active material layer becomes highly resistant, the short circuit current decreases, and the amount of heat generated can be reduced. In this way, the battery of the present disclosure can continue to discharge (reducing the SOC) even after a short circuit while suppressing a temperature rise, thereby improving safety during a short circuit.

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 oxygen release from the positive electrode active material layer can be suppressed. In addition, the above-mentioned Patent Document 2 discloses providing a high heat capacity member on the 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 also an advantage in terms of energy density.

1. Cell The cell in the present disclosure has 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. In the cell in the present disclosure, the negative electrode active material layer contains lithium titanate. Details of each member will be described later.

In addition, in the present disclosure, the positive electrode current collector has fusing characteristics that make it easier to fuse than the negative electrode current collector. Such fusing characteristics can be adjusted, for example, by changing at least one of the thickness of the current collector and the melting point of the current collector.

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.

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.

When the thickness T1 of the negative electrode collector is thicker than the thickness T2 of the positive electrode collector, T2/T1 is, for example, 0.40 or more, and may be 0.50 or more. On the other hand, T2/T1 is, for example, 0.95 or less, and may be 0.80 or less, 0.70 or less, or 0.60 or less.

When the thickness T1 of the negative electrode collector is thicker than the thickness T2 of the positive electrode collector, T1-T2 is, for example, 1 μm or more, and may be 5 μm or more, 10 μm or more, or 20 μm or more. On the other hand, T1-T2 is, for example, 100 μm or less, and may be 50 μm or less.

When the melting point M1 of the negative electrode collector is higher than the melting point M2 of the positive electrode collector, M2/M1 is, for example, 0.10 or more, or may be 0.30 or more, or may be 0.50 or more. On the other hand, M2/M1 is, for example, 0.95 or less, or may be 0.70 or less.

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.

(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.

Lithium titanate is a compound containing at least Li, Ti and O elements. At least one of Li and Ti may be partially substituted with other elements. 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 is particularly preferred. The negative electrode active material layer may contain only one type of lithium titanate, or may contain two or more types of lithium titanate.

The lithium titanate may be in the form of particles, for example, and has a particle diameter (D ₅₀ ) of, for example, 0.5 μm or more and 5 μm or less.

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

Examples of conductive materials include carbon materials such as acetylene black (AB), ketjen black (KB), carbon fiber, carbon nanotube (CNT), and carbon nanofiber (CNF). Examples of binders 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 electrolytes include the same materials as those described in "(4) Electrolyte Layer".

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

(2) Negative electrode current collector and positive electrode current collector The material and thickness of the negative electrode current collector and 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 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 positive electrode current collector include a foil shape, a mesh shape, and a porous shape.

(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."

The positive electrode active material is not particularly limited, and examples thereof include oxide active materials. Examples of the oxide active material include rock salt layer type active materials such as _LiCoO2 , _LiMnO2 , _LiNiO2 , _LiVO2 , and LiNi1 _{/ 3Co1/ 3Mn1 / 3O2 ,} spinel type active materials such as _LiMn2O4 , _Li4Ti5O12 , and _{Li ( Ni0.5Mn1.5} ) _O4 , and olivine type active materials such as _LiFePO4 , _LiMnPO4 , _LiNiPO4 , and _LiCoPO4 .

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

(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."

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

The thickness of the electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

2. Battery The battery in the present disclosure includes the above-mentioned cell. 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.

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

Applications of the battery in this disclosure include, for example, power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered automobiles, and diesel-powered automobiles. The battery in this disclosure may also be used as a power source for moving objects other than vehicles (e.g., trains, ships, and aircraft), and may also be used as a power source for electrical products such as information processing devices.

This disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and anything that has substantially the same configuration as the technical ideas described in the claims of this disclosure and has similar effects is included within the technical scope of this disclosure.

[Example 1]
An all-solid-state battery (evaluation battery) was produced 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. The negative electrode active material layer was a layer containing a negative electrode active material (Li ₄ Ti ₅ O ₁₂ ), a binder (PVdF-based binder), a sulfide solid electrolyte (Li ₂ S-P ₂ S ₅ -based glass ceramic containing LiBr and LiI), and a conductive material (VGCF). The positive electrode active material layer was a layer containing a positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), a binder (PVdF-based binder), a sulfide solid electrolyte (Li ₂ S-P ₂ S ₅ -based glass ceramic containing LiBr and LiI), and a conductive material (VGCF). The solid electrolyte layer was a layer containing a binder (butadiene rubber) and a sulfide solid electrolyte (Li ₂ S-P ₂ S ₅ -based glass ceramic containing LiBr and LiI). 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.

[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.

[Reference Example 1]
With reference to the examples of the above-mentioned Patent Document 2 (JP 2016-207614 A), a battery having a high heat capacity member (copper foil) was produced.

[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 a 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 was lowered 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 was progressing 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.

(Energy density)
The energy density of the batteries obtained in Examples 1 and 2 and Reference Example 1 was evaluated. The results are shown in Table 1.

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.

Reference Signs List 1 negative electrode current collector 2 negative electrode active material layer 3 electrolyte layer 4 positive electrode active material layer 5 positive electrode current collector 10 cell 20 battery

Claims (1)

A battery including a cell having, 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,
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 positive electrode active material layer contains LiNi1 _/ 3Co1 _/ 3Mn1 _/ 3O2 as _a positive electrode active material.