JP2003036825A - Nonaqueous electrolyte solution battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte solution battery with high safety by forming terminal structure capable of preventing or restraining a spark which may be generated in a terminal portion caused by leakage of nonaqueous electrolyte solution. SOLUTION: The nonaqueous electrolyte solution battery 1 which has a structure having a battery case 20 made from metal, outer terminals 30b, 40b insulated therefrom, and fix member 32, 33, 42 and 43 fixing the outer terminals is so constituted that the outer terminal 30b existing in at least positive side is formed from aluminum alloy material and its fix member 32, 33 is formed from aluminum alloy material or electrical insulating material. Even if the nonaqueous electrolyte solution leaks in its portion B to form a bridge, an active radical promoted by the ionization of transition metal is less generated and an organic catalyst is restrained to dissociate, and thus the spark is prevented or restrained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte battery containing a non-aqueous electrolyte, and more particularly to a non-aqueous electrolyte battery excellent in safety when it leaks.

[0002]

2. Description of the Related Art Non-aqueous electrolyte batteries such as lithium secondary batteries have a high battery voltage and a high energy density. In the fields of information-related equipment and communication equipment, they have been put into practical use and widely spread as power supplies used for these equipment. On the other hand, also in the field of automobiles, the development of electric vehicles has been rushed due to environmental problems and resource problems, and non-aqueous electrolyte batteries such as lithium secondary batteries are also being considered as a power source for this electric vehicle. ing.

However, since the non-aqueous electrolyte battery uses a non-aqueous electrolyte solution using an organic solvent as an electrolyte solution as a constituent element, it is necessary to give sufficient consideration to its safety. Leakage of the non-aqueous electrolyte is a phenomenon that should be avoided, but it is desired that sufficient safety be ensured even if leakage occurs without stopping.

In a non-aqueous electrolyte battery, a positive electrode and a negative electrode are housed in a battery case together with a non-aqueous electrolyte solution. Generally, the battery case has a structure in which external terminals are provided for conducting the positive electrode and the negative electrode, respectively. I am doing it. The external terminal is often attached to the battery case while being insulated from the battery case and fixed to the battery case by a fixing member such as a nut. In that case, a part of the boundary between the external terminal and the battery case, that is, the boundary is sealed with some kind of sealing member to prevent leakage of the non-aqueous electrolyte from that part as much as possible. A metal material is preferably used for the battery case because it has good mechanical strength, heat resistance, etc. In that case, the battery case is often grounded.

In a non-aqueous electrolyte battery having such a terminal structure, in the unlikely event that the non-aqueous electrolyte leaks from this seal portion, the external terminals that should be electrically insulated are exposed. The leaked non-aqueous electrolytic solution comes into contact with both the portion and the battery case, or both the fixing member and the battery case, to form a bridge. If this non-aqueous electrolyte battery is charged and discharged with such a bridge of non-aqueous electrolyte present, sparks may occur at the portion of the bridge. If the non-aqueous electrolyte battery is used alone in one cell, the voltage applied to the bridge portion is high when using multiple cells combined in series.
The likelihood of sparks increases. Since this spark impairs the safety of the non-aqueous electrolyte battery, it is urgently desired to prevent or suppress it.

[0006]

The present inventor has obtained one finding regarding the cause of the spark. What is that knowledge?
The member forming the terminal portion is a trigger for generating a spark. Therefore, the mechanism of spark generation considered by the inventor will be described below by taking a lithium secondary battery, which is one of the non-aqueous electrolyte batteries, as an example.

In a lithium secondary battery, a current collector on the positive electrode side is generally used for reasons such as electrochemical stability against the potential difference between the positive electrode and the negative electrode, economical efficiency, etc. inside the battery in contact with the non-aqueous electrolyte. The current collecting leads, internal terminals, etc. are made of an aluminum-based material, and the current collectors, current collecting leads, internal terminals, etc. on the negative electrode side are made of a copper-based material. The external terminal that communicates with the internal terminal is usually formed integrally, and the external terminal is formed of an aluminum-based material on the positive electrode side and a copper-based material on the negative electrode side. Further, the battery case is often formed of a stainless steel-based material in consideration of mechanical strength, economy and the like. The fixing member for fixing and attaching the external terminal to the battery case is generally made of an iron-based material in consideration of economical efficiency, etc. Usually, this fixing member has a nut shape. Since it is screwed onto a part of the external terminal, it is electrically connected to the external terminal and insulated from the battery case.

In the lithium secondary battery having such a structure, when the non-aqueous electrolyte leaks and a bridge is formed at the terminal portion, specifically between the fixing member and the battery case, the potential difference existing between the two causes , Decomposition of the non-aqueous electrolyte occurs. A part of the non-aqueous electrolyte is oxidized into a peroxide on the surface of the member having the higher potential, that is, the positive side, and active radicals are generated from this. To generate this active radical,
The presence of transition metals such as Cu, Fe and Ni has a great influence. More specifically, when these transition metals are ionized, they act as a catalyst for initiating an autoxidation reaction (radical reaction) of an organic substance and promote the generation of active radicals. When the energized state continues for a long time and the liquid temperature rises, organic matter containing these radicals, particularly an organic solvent, undergoes ion dissociation in the atmosphere, resulting in the generation of sparks. This is the mechanism of spark generation known to the present inventor.

Therefore, it is considered that the sparks due to the above mechanism can be prevented or suppressed by appropriately selecting the material of the member forming the terminal portion, especially the member forming the terminal portion on the positive electrode side. Came to. The present invention provides a highly safe non-aqueous electrolyte battery by providing a terminal structure capable of preventing or suppressing the above-mentioned spark that may occur in the terminal portion due to leakage of the non-aqueous electrolyte. This is an issue.

[0010]

(1) A non-aqueous electrolyte battery according to the present invention is a non-aqueous electrolyte battery in which a positive electrode and a negative electrode are housed together with a non-aqueous electrolyte in a metal battery case. , At least on the positive electrode side, an external terminal that is insulated from the battery case, is attached to the battery case, and at least the exposed portion is formed of an aluminum alloy; and the external terminal is fixed to the battery case and at least the exposed portion Has a terminal structure provided with a fixing member made of a material selected from an aluminum alloy and an electrically insulating substance (corresponding to claim 1).

That is, the non-aqueous electrolyte battery of the present invention limits the material of the member forming the terminal portion on the positive electrode side, particularly the material of the exposed portion. Generally, assuming that the battery case is grounded (grounded), when a bridge of non-aqueous electrolyte is formed between the terminal part on the positive electrode side and the battery case, the positive electrode terminal side has a high potential, that is, It will be the plus side. Since the material of the external terminal on the positive electrode side and the fixing member on the positive electrode side that fixes it is very small, even if it does not contain transition metal, the non-aqueous electrolyte leaks to that part and bridges are formed. Even when it is formed, the ionization of the transition metal is less likely to promote the generation of the active radical, the dissociation of the organic solvent is suppressed, and the spark is prevented or suppressed. Therefore, the non-aqueous electrolyte battery ensures high safety even if the non-aqueous electrolyte leaks.

(2) The type of the non-aqueous electrolyte battery to which the present invention is applied is particularly limited as long as the positive electrode and the negative electrode are housed together with the non-aqueous electrolyte in a metal battery case. Not a thing. For example, a lithium ion secondary battery or a lithium polymer secondary battery in which a positive electrode using a lithium transition metal composite oxide as an active material and a negative electrode using a carbon material as an active material are combined, and a metallic lithium using metallic lithium as the negative electrode. Lithium secondary battery such as secondary battery, L
The target is various secondary batteries such as a secondary battery using an element other than i, for example, Na or Mg as a carrier. Further, not only a rechargeable secondary battery but also a primary battery capable of only discharging may be used. Further, the shape of the battery is various, such as a cylindrical shape and a rectangular shape.

In the terminal structure which is a characteristic part of the non-aqueous electrolyte battery of the present invention, the external terminal may be integrally formed with the internal terminal, in which case one terminal is the external terminal portion and the internal terminal. And a part. Therefore, in this specification, the external terminal is meant to include such an aspect. Further, the fixing member is a member having a function of fixing the external terminal to the battery case, and its form is not particularly limited. For example, a nut having a male screw formed on the external terminal and having a female screw that is screwed onto the male screw is generally used. However, by caulking, adhering, welding, etc., the external terminal can be used as a battery case. It may be fixed to. Furthermore, the auxiliary member such as a washer is also included in the fixing member. The fixing member may be electrically connected to either the external terminal or the battery case. In the case of a nut that is screwed to the external terminal, it conducts with the external terminal,
The nut and the battery case need to be electrically insulated.

The exposed portion of the external terminal and the fixing member means a portion that comes into contact with the outside air, and means a portion that forms a bridge when the non-aqueous electrolyte leaks. If this portion is an external terminal, it may be made of an aluminum alloy, and if it is a fixing member, it may be made of an aluminum alloy and an electrically insulating substance. Therefore, instead of being formed of a single material, the exposed portion may be formed of the material, for example, by coating. However, some of the external terminals
It is necessary to be electrically conducted to be connected to an external device for power supply and the like, and at least a portion thereof needs to have an aluminum alloy material exposed. Various materials such as ceramics, resins, plastics, and rubbers can be selected as the electrically insulating material according to the purpose.

(3) In the non-aqueous electrolyte battery of the present invention, at least the positive electrode side has the above-mentioned terminal structure, and the terminal structure on the negative electrode side is not limited. For example, there may be a case where the negative electrode terminal and the battery case are electrically connected, or a case where the battery case also serves as the negative electrode external terminal. When the non-aqueous electrolytic solution leaks, the terminal portion on the positive electrode side, which is often at a high potential, has the above structure, so that the safety is significantly improved.

However, even on the negative electrode side, the nonaqueous electrolytic solution may form a bridge in a state where the terminal portion has a high potential. For example, this is a case where the battery case is grounded by an assembled battery in which a plurality of cells are combined. In such a case, in the terminal portion on the negative electrode side of the battery located on the high potential side, the leaked non-aqueous electrolyte solution forms a bridge between the terminal portion and the battery case.

If such a case is also assumed, it is desirable that the non-aqueous electrolyte battery of the present invention is implemented in a mode in which both the positive electrode side and the negative electrode side have the terminal structure (claim 2). Correspondence). By carrying out in this manner, even when the terminal portion on the negative electrode side has a high potential with respect to the battery case, the generation of the active radical is less promoted by the ionization of the transition metal, and the dissociation of the organic solvent is suppressed. As a result, sparks are prevented or suppressed. Therefore, when both the positive electrode side and the negative electrode side have the above terminal structure, the safety is further enhanced.

For example, in the case of a lithium secondary battery, as described above, the internal terminal of the negative electrode is often formed of a copper-based material, and the external terminal integrated with the same is often formed of a copper-based material. In such a case, the exposed parts should be made of aluminum-based material in order to ensure electrical continuity with external equipment, such as by plating the parts that will become the external terminals with aluminum. Is possible.

(4) Further, the non-aqueous electrolyte battery of the present invention comprises
It is desirable that the battery case be made of an aluminum alloy (corresponding to claim 3). Considering the potential difference existing between the external terminal and the battery case, the terminal side does not always have a high potential. For example, when the battery case is grounded so that it has the same potential as the positive electrode with the highest potential, when the non-aqueous electrolyte forms a bridge between the battery case and the battery case at the terminal, the battery case side is on the high potential side. Becomes In such a case, when the battery case is formed of a material containing a large amount of transition metal such as stainless steel, the generation of the active radical is promoted by the ionization of many transition metals contained in this material, and the organic solvent such as an organic solvent may be generated. The dissociation leaves the potential for sparking.
Therefore, in the non-aqueous electrolyte battery of the present invention in which the battery case is also formed of an aluminum-based material, sparks in such a case are also prevented or suppressed, and safety is further enhanced.

(5) When the exposed portions of the external terminals and the fixing member and the battery case are made of an aluminum alloy, the aluminum alloy is Cu as a main alloying element.
It is desirable that it does not include (corresponding to claim 4). For example, in the stretched material, the JIS 2000-based aluminum alloy is an Al—Cu—Mg-based aluminum alloy, and there are alloys containing Cu as a main alloying element, such as such an alloy. Among transition metals, Cu has a high ability as a catalyst for initiating the above-described organic substance autoxidation reaction (radical reaction), and an aluminum alloy containing Cu as a main alloying element, that is, an aluminum alloy having a high Cu content is slightly However, the effect of preventing or suppressing sparks is small. Therefore, if the above member is formed from an aluminum alloy material that does not contain Cu as a main alloying element, the effect of preventing or suppressing the spark becomes sufficiently large.

Specifically, pure aluminum (1000
System), Al-Mg-based alloy (5000-based), Al-Mn-based alloy (3000-based), and the like. In addition,
Since pure aluminum can be expected to have sufficient safety, the constituent members may be formed of pure aluminum.
Therefore, in the present specification, the “aluminum alloy” means a broad concept including pure aluminum.

In addition, regardless of whether or not Cu is contained as a main alloying element, when the above-mentioned constituent parts are formed from an aluminum alloy material, corrosion is generated on the surface of the non-aqueous electrolyte when the non-aqueous electrolyte bridges and is energized. It has been confirmed that products (specifically, aluminum hydroxide, aluminum fluoride, etc.) have high insulating properties, and from that point as well, sparks are less likely to occur compared to metal materials based on transition metal elements. A highly safe non-aqueous electrolyte battery can be constructed.

(6) The non-aqueous electrolyte battery of the present invention comprises a positive electrode and a negative electrode, together with the non-aqueous electrolyte solution, housed in a metal battery case. The non-aqueous electrolytic solution is a solution in which an electrolyte is dissolved in an organic solvent. In this case, the electrolyte is not particularly limited, but it is desirable that the electrolyte contains LiBF ₄ (corresponding to claim 5).

In the case of forming the above-mentioned components from an aluminum alloy material, the present inventor has found that the spark can be further prevented or suppressed by further limiting the type of electrolyte. This depends on the electrolyte used when a positive potential is applied to the metal material.
This is probably because the degree of elution of metal ions is different. That is, the anode polarization characteristics of the metal material differ depending on the electrolyte used. For example, in the case of a lithium secondary battery, the electrolyte contains LiI, LiClO ₄ , LiAsF ₆ , and LiB that dissolves in an organic solvent to generate lithium ions.
F ₄ , LiPF ₆ or the like can be used. As will be described later in detail in Examples, it was found that when an electrolyte containing LiBF ₄ was used, the generation of sparks could be effectively suppressed. According to the experiment described later, when an electrolyte containing LiBF ₄ is used, even if a positive potential is applied to the aluminum alloy material, elution of metal ions such as aluminum is small. That is, it is considered that the passive film of the aluminum alloy material is stably maintained in the presence of LiBF ₄ . For this reason, even if the non-aqueous electrolyte solution leaks, it is difficult for the current to flow, and the temperature rise at the leaking portion is small. Therefore, the evaporation of the non-aqueous electrolyte that promotes the generation of sparks, the generation of combustible gas due to the decomposition of the non-aqueous electrolyte, and the like are suppressed.

[0025] (7) is used LiBF ₄ electrolyte containing, the content of LiBF ₄ in the electrolyte, (corresponding to claim 6) 20 is desirably mol% or more when the whole electrolyte is 100 mole% . This is because when the content of LiBF ₄ is less than 20 mol%, the passivation film of the aluminum alloy material is not sufficiently stabilized and the above spark suppressing effect cannot be sufficiently obtained. In order to further enhance the effect of suppressing sparks, LiB in the electrolyte
It is desirable to increase the content ratio of F ₄ . LiBF ₄
It is more preferable that the content ratio of is 50 mol% or more.
Further, it is more preferable that the content ratio of LiBF ₄ is 100 mol%, that is, LiBF ₄ alone is used as the electrolyte.

On the other hand, as the organic solvent, an aprotic organic solvent such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolane, methylene chloride, or the like, or Two or more kinds of these solvents can be used. The organic solvent has a high dielectric constant in order to promote dissociation of the lithium salt that is the electrolyte, and
A low viscosity is required so as not to hinder the movement of lithium ions. From this point of view, it is desirable to use, for example, ethylene carbonate or the like as the high dielectric constant solvent and diethyl carbonate or the like as the low viscosity solvent.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a cylindrical lithium secondary battery having a relatively large capacity as an embodiment of the non-aqueous electrolyte battery of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a cross section of the lithium secondary battery.

The lithium secondary battery 1 includes an electrode body 10 and
Battery case 2 for sealing the electrode body 10 together with the non-aqueous electrolyte
0, and a positive electrode terminal 30 and a negative electrode terminal 40 attached to the battery container 20 and electrically connected to the electrode body 10.
The electrode body 10 includes a sheet-shaped positive electrode 11 and a sheet-shaped negative electrode 1.
2 and 2 are sandwiched by a separator 13 and wound around a winding core 14 to form a roll shape.

The positive electrode 11 is prepared by first mixing a lithium-transition metal composite oxide as a positive electrode active material, graphite as a conductive material, and polyvinylidene fluoride as a binder, and mixing N-methyl-2- in an appropriate amount as a solvent. Add pyrrolidone,
These are sufficiently kneaded to prepare a paste-like positive electrode mixture, and then this positive electrode mixture is applied to both surfaces of an aluminum foil current collector having a thickness of 15 μm, dried, and pressed to increase the density of the positive electrode mixture. It was made by doing.

For the negative electrode 12, a carbon material as a negative electrode active material and polyvinylidene fluoride as a binder are mixed, and an appropriate amount of N-methyl-2-pyrrolidone is added as a solvent,
These are sufficiently kneaded to prepare a paste-like negative electrode mixture, and then this negative electrode mixture is applied to both sides of a copper foil current collector having a thickness of 10 μm, dried, and pressed to increase the density of the negative electrode mixture. It was made by doing.

The separator 13 is a porous polypropylene sheet having a thickness of 25 μm, and two sheets thereof were used.
The winding core 14 includes an aluminum winding core portion 14a made of an aluminum alloy, which is located on the positive electrode terminal side, and a resin winding made of resin, which is coaxially screw-connected to the aluminum winding core portion 14a and is located on the negative electrode terminal side. It is composed of a core portion 14b.

The electrode body 10 produced by winding the positive electrode 11 and the negative electrode 12 on the winding core 14 by sandwiching the separator 13 therebetween, and winding the positive electrode 11 and the negative electrode 12 into the positive electrode lead 11a. And a negative electrode lead 12a are attached, and these leads 11a and 12a are used for the electrode body 10.
Of each of the winding ends.

The battery case 20 is made of aluminum alloy (A
3003) made of a cylindrical outer can, and an aluminum alloy (A10) to be joined to both open ends of the outer can, respectively.
50) Disc-shaped positive electrode side cover plate 22 and negative electrode side cover plate 2
3 and 3. The plate thickness of the outer can 21 is 1.5 mm,
Its outer diameter is 33 mm and its length is 170 mm. The positive electrode side cover plate 22 and the negative electrode side cover plate 23 have a plate thickness of 1.5 mm, and have a disk shape having an outer diameter substantially equal to the inner diameter of the outer can 21. The outer can 21 is joined to the positive electrode side cover plate 22 and the negative electrode side cover plate 23 by laser welding all around the area A in the figure.

Each of the positive electrode side cover plate 22 and the negative electrode side cover plate 23 is provided with a safety valve 24 that opens when the internal pressure of the battery case 20 exceeds a predetermined pressure (the positive electrode side is not shown). Further, the negative electrode side cover plate 23 is further provided with an electrolytic solution injection port 25, and an injection hole plug 26 for sealing the electrolytic solution injection port 25 is screwed and attached.

The positive electrode terminal 30 is made of aluminum alloy (A1
050), and is composed of a current collector 30a serving as an internal terminal and a bolt-shaped external terminal 30b. The current collector 30a is screw-connected to the aluminum winding core 14a of the winding core 14; The external terminal portion 30b has a positive electrode terminal mounting hole 22a provided in the positive electrode side cover plate 22 of the battery case 20 in a state where the tip of the external terminal portion 30b is projected to the outside of the battery.
Through the gasket 31 made of E), the aluminum alloy (A
It is attached by a washer 32 made of 5052) and a nut 33 made of an aluminum alloy (A5052), and is insulated from the battery case 20. Current collector 3
A strip-shaped positive electrode lead 11 extending from the electrode body 10 is provided at 0a.
a is joined to the periphery thereof to ensure electrical continuity between the positive electrode terminal 30 and the positive electrode 11. That is, in the present lithium secondary battery, the external terminal portion 30b serves as the "external terminal" on the positive electrode side, and the washer 32 and the nut 33 serve as the "fixing member" on the positive electrode side.

The negative electrode terminal 40 is made of a copper alloy and comprises a current collecting portion 40a serving as an internal terminal and a bolt-shaped outer terminal portion 40b. The current collecting portion 40a is a resin winding core portion of the winding core 14. 1
4b, and the external terminal portion 40b is connected to the PTFE terminal in the negative electrode terminal mounting hole 23a provided in the negative electrode side cover plate 23 of the battery case 20 with the tip protruding outside the battery.
Through an aluminum alloy (A50
52) washer 42, aluminum alloy (A505
It is attached by a nut 43 made in 2), and is insulated from the battery case 20. Incidentally, the external terminal portion 40b is plated with aluminum, and the exposed portion is formed of aluminum. A strip-shaped negative electrode lead 12a extending from the electrode body 10 is joined to the periphery of the current collector 40a to ensure electrical conduction between the negative electrode terminal 40 and the negative electrode 12. That is, in the present lithium secondary battery, the external terminal portion 40b serves as the "external terminal" on the negative electrode side, and the washer 42 and the nut 43 are provided.
Is the "fixing member" on the negative electrode side.

As the non-aqueous electrolyte to be injected, LiBF ₄ was dissolved at a concentration of 1 M in a mixed organic solvent in which ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 3: 7. Here, when the gasket 31 on the positive electrode side or the gasket 41 on the negative electrode side is loosened for some reason, the non-aqueous electrolyte solution leaks from that portion. In that case, the non-aqueous electrolyte is accumulated in the portion B or C in the drawing, and in that portion, between the external terminal, the fixing member and the battery case 20, more specifically, on the positive electrode side. If there is, external terminal portion 30b, washer 32, washer 32
Between at least one of the external terminal portion 40b, the washer 42, and the nut 43 and the negative electrode side cover plate 23 on the negative electrode side.
A bridge is formed. In this state, even if the present lithium secondary battery 1 is charged or discharged, the generation of active radicals is not promoted by the ionization of transition metals such as Fe and Ni, and the dissociation of the organic solvent of the non-aqueous electrolytic solution is not promoted. It will be suppressed and sparks will be prevented or suppressed. Moreover, since LiBF ₄ is used as the electrolyte, almost no current flows. Therefore, the temperature rise in the portion where the non-aqueous electrolyte is accumulated is small, and the evaporation of the non-aqueous electrolyte that promotes the generation of sparks and the generation of combustible gas due to the decomposition of the non-aqueous electrolyte are suppressed. That is, the present lithium secondary battery 1 is a battery with extremely high safety when a non-aqueous electrolyte leaks.

Although the embodiment of the non-aqueous electrolyte battery of the present invention has been described above, the above-described embodiment is only one embodiment, and the non-aqueous electrolyte battery of the present invention includes the above-described embodiment as a starting point. It can be implemented in various forms with various changes and improvements based on the knowledge of those skilled in the art.

[0039]

Example A lithium secondary battery was actually manufactured, various leaks of non-aqueous electrolyte were schematically reproduced, and various experiments were performed to confirm the occurrence of sparks. In addition, an energization experiment was conducted in a non-aqueous electrolyte in order to investigate the degree of spark generation due to the difference in materials. Furthermore, a current-carrying experiment was conducted in a non-aqueous electrolyte in order to investigate the degree of spark generation due to the difference in electrolyte. Experiments were also conducted to investigate the stability of the passive state of various materials. These will be described below.

<Experiment 1> The experiment described here was carried out by manufacturing a prismatic lithium secondary battery. The appearance of the manufactured lithium secondary battery is shown in FIG. In this lithium secondary battery, an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween is housed in a square battery case 20 made of SUS304 together with a non-aqueous electrolytic solution, and a positive electrode side and a negative electrode are provided on top. Side terminal portion is present, and the positive electrode side terminal portion is
The external terminal 30b made of an aluminum alloy (A1050) on which a male screw is formed, a PTFE gasket 31 that seals the external terminal 30b, and a nut 33 (material of which is a fixing member that is screwed into the external terminal 30b and fixed thereto) It will be described later). The external terminal 30b and the nut 33 are insulated from the battery case 20 by the gasket 31. The terminal portion on the negative electrode side serves as an external terminal 40b made of a copper alloy on which a male screw is formed, a gasket 41 made of PTFE that seals the external terminal 40b, and a fixing member that is screwed to the external terminal 40b to fix it. It is composed of a nut 43 made of steel. Note that, as with the positive electrode side, the gasket 41
Thus, the external terminal 40b and the nut 43 are insulated from the battery case 20.

A brief description of the internal structure of the battery is as follows.
The positive electrode is LiNi, which is the positive electrode active material. _0.8Co_0.15Al
_0.05O₂And carbon black as a conductive material, and a binder
Suitable for use as a solvent by mixing with polyvinylidene fluoride as
Add N-methyl-2-pyrrolidone in an amount to fill them.
To prepare a paste-like positive electrode mixture, and then
Apply this positive electrode mixture on both sides of the aluminum foil current collector,
It was dried and pressed to increase the density of the positive electrode mixture.
It is a thing. In addition, the negative electrode is a graphitized film that becomes the negative electrode active material.
Sophase microspheres and polyvinylidene fluoride as a binder
And N-methyl-2-pyrolone as a solvent.
Add ridone and knead them thoroughly to form a paste.
Prepare a negative electrode mixture, and then use this negative electrode mixture with a copper foil current collector.
Apply to both sides of the anode and dry to increase the density of the negative electrode mixture.
It was made without any pressure. The separator is porous
A sheet made of polyethylene is used. The positive and negative electrodes
The electrode body wound with the separator interposed between it and the positive electrode
Conductive between the polar terminal and the negative electrode current collector and the negative terminal
It is stored. Non-aqueous electrolyte is ethylene carbonate
And diethyl carbonate were mixed in a volume ratio of 3: 7.
LiPF in mixed solvent₆Was dissolved at a concentration of 1M
Using. From this configuration, the present lithium secondary battery is
A lithium secondary battery having a terminal voltage of 2 to 3.0 V, and
Has become.

Two types of lithium secondary batteries were prepared, each having a different material for the nut 33 on the positive electrode side, which serves as a fixing member.
One of them is that the nut 33 is made of aluminum alloy (A5
052) formed of a material, and the other is formed of a stainless (SUS304) material. Hereinafter, the one using an aluminum alloy nut as the fixing member on the positive electrode side is referred to as the lithium secondary battery of Example 1, and the one using the stainless nut is referred to as the lithium secondary battery of Comparative Example 1.

As shown in FIG. 3, 28 lithium secondary batteries were connected in series to form two sets of assembled batteries. The battery cases of the lithium secondary batteries on the highest potential side and the lowest potential side were grounded, assuming the use of actual assembled batteries. Then, each assembled battery was fully charged, and then a load R was connected and discharged.
At the start of this discharge, in order to simulate the leakage of the non-aqueous electrolyte, the portion of the gasket 31 on the positive electrode side, which is the highest potential side (see FIG. 2).
And the position of D in FIG. 3), the same non-aqueous electrolyte solution stored in the battery case is dropped, and the nut 33 and the battery case 20
A non-aqueous electrolyte bridge was formed between and. In this way, discharge of each assembled battery was continued.

In the assembled battery composed of the lithium secondary battery of Comparative Example 1, after a while, sparks were generated from the portion where the non-aqueous electrolyte was dropped. On the other hand, in the assembled battery composed of the lithium secondary battery of Example 1, no spark was observed, although heat was generated and some gas was generated from that portion. From the results of this experiment, in the positive electrode side terminal portion, in the non-aqueous electrolyte battery of the present invention in which the external terminal is formed of an aluminum alloy material and the fixing member is formed of an aluminum alloy material, the occurrence of sparks is prevented or It was proved that it was suppressed and the safety was high when the non-aqueous electrolyte leaked. Further, from this result, it can be easily inferred that the generation of sparks can be prevented or suppressed even in that portion by configuring the terminal portion on the negative electrode side in the same manner, and the non-aqueous electrolyte battery having higher safety It turns out that

<Experiment 2> As in the case of Experiment 1, an experiment was conducted to confirm the occurrence of sparks by constructing an assembled battery.
The non-aqueous electrolyte battery used in this experiment is the lithium secondary battery having the structure shown in FIG. 1 described above. The battery case 20
The outer can 21, the positive electrode side cover plate 22 and the negative electrode side cover plate 23, which are the constituent members, were formed from an aluminum alloy (A1050) material. Further, the external terminal portion 40b on the negative electrode side is formed of a copper alloy material and is not plated with aluminum. The washer 32 was omitted from the fixing member of the positive electrode terminal portion, and the positive electrode terminal 30 was fixed only by the nut 33. The material of the nut 33 will be described later. Similarly, the washer 42 was omitted from the fixing member of the negative electrode terminal portion, and the negative electrode terminal 40 was fixed only by the polypropylene (PP) nut 43.

Briefly referring to the constitutions of the positive electrode and the negative electrode, the positive electrode is prepared by mixing LiMn ₂ O ₄ as a positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride as a binder, and as a solvent. A proper amount of N-methyl-
2-Pyrrolidone was added, and these were sufficiently kneaded to prepare a positive electrode mixture material in the form of a paste, and then this positive electrode mixture material was applied to both surfaces of an aluminum foil current collector and dried to obtain a positive electrode mixture material density. It was made by pressing to raise it. Further, the negative electrode is a mixture of graphitized mesophase spherules serving as a negative electrode active material and polyvinylidene fluoride as a binder,
An appropriate amount of N-methyl-2-pyrrolidone was added as a solvent, and these were sufficiently kneaded to prepare a paste-like negative electrode mixture, and then this negative electrode mixture was applied to both surfaces of the copper foil current collector, It was prepared by drying and pressing to increase the density of the negative electrode mixture. A porous polyethylene sheet is used as the separator. As in the case of Experiment 1, the non-aqueous electrolytic solution was prepared by adding LiPF 6 to a mixed solvent prepared by mixing ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7.
What melt | dissolved ₆ in the density | concentration of 1M was used. With this configuration, the present lithium secondary battery is also a lithium secondary battery having a terminal voltage of 4.2 to 3.0V.

Two types of lithium secondary batteries were produced, each having a different material for the nut 33 serving as a fixing member on the positive electrode side.
One is made of PP and the other is made of nickel-plated steel. In the following, the one using a PP nut as the fixing member on the positive electrode side is used in Example 2.
The lithium secondary battery of Comparative Example 2 uses a nickel-plated steel nut.

As in Experiment 1, 28 lithium secondary batteries were connected in series to form two sets of assembled batteries. The battery cases of the lithium secondary batteries on the highest potential side and the lowest potential side were grounded, assuming the use of actual assembled batteries. Then, each assembled battery was fully charged, and then a load was connected and discharged.
At the start of this discharge, in order to simulate leakage of the non-aqueous electrolyte solution, the same non-aqueous electrolyte solution as the one housed in the battery case is placed in the gasket part (position B in FIG. 1) on the positive electrode side, which is the highest potential side. Was dropped to form a bridge of the non-aqueous electrolyte between the nut 33 and the battery case 20. In this way
The discharge of each assembled battery was continued.

In the assembled battery composed of the lithium secondary battery of Comparative Example 2, after a while, sparks were generated from the portion where the non-aqueous electrolyte was dropped. On the other hand, in the assembled battery composed of the lithium secondary battery of Example 2, sparks were not observed although heat was generated and some gas was generated from that part. From the results of this experiment, in the positive electrode side terminal portion, in the non-aqueous electrolyte battery of the present invention in which the external terminal is formed of an aluminum alloy material and the fixing member is formed of an electrically insulating substance, the occurrence of sparks is prevented. Alternatively, it was suppressed, and it was proved that safety is high when the non-aqueous electrolyte leaks. Further, as in the case of Experiment 1, it can be easily inferred from this result that the generation of sparks can be prevented or suppressed even in that portion by configuring the terminal portion on the negative electrode side to have the same configuration, which is more safe. It can be seen that a high-performance non-aqueous electrolyte battery can be obtained.

<Experiment 3> Various experiments are performed in the experiment described here.
Non-aqueous electrolysis conducted to investigate the degree of sparking of materials
It is an energization experiment in a liquid. Formed from various materials
4cm made ²From the plate with the area of
Use and sandwich a 1 mm thick PTFE sheet between them
Then, the electrode body was constructed. This electrode body is 100mL beaker
And place 10 mL of non-aqueous electrolyte into the electrode body.
Soaked The non-aqueous electrolyte is ethylene carbonate and diethyl ether.
A mixed solvent obtained by mixing a carbonate with a volume ratio of 3: 7
And LiPF₆Is dissolved at a concentration of 1M. So
Then connect the power supply to each electrode plate of the electrode assembly, and
Applying a constant voltage of 100V for 20 minutes
A test was conducted to examine the occurrence of sparks. The conclusion of this experiment
As a result, the material of the electrode plate on the + side, that is, the high potential side, is shown in Table 1 below.
Quality, the material of the negative side plate, that is, the low potential side, and those
The degree of spark generation in the electrode assembly
You

[0051]

[Table 1]

As can be seen from Table 1 above, the degree of spark generation largely depends on the material of the material on the + side, that is, the high potential side. Then, when an alloy material having a transition metal such as stainless (iron), nickel, or copper as a central element is present on the high potential side, a large spark is generated. On the other hand, it can be confirmed that sparks do not occur in the aluminum alloy material, or if sparks occur, they are slight. From this, forming the external terminal and its fixing member, further, the battery case from an aluminum alloy material is effectively prevented or suppressed from generating a spark even when the non-aqueous electrolyte leaks,
It can be confirmed that a highly safe non-aqueous electrolyte battery can be constructed. It should be noted that even among aluminum alloys, when a transition metal element is not included as a main alloy element, that is, when a 1000 series, 5000 series, or 3000 series aluminum alloy having a relatively low Cu content is used, the safety is higher. Can also be confirmed.

<Experiment 4> Similar to the case of Experiment 1, an experiment was conducted to confirm the occurrence of sparks by constructing an assembled battery.
The non-aqueous electrolyte battery used in this experiment is, in addition to the lithium secondary battery of Example 1 above, two types of lithium secondary batteries different from the above only in the electrolyte. Specifically, the electrolyte forming the non-aqueous electrolyte in the lithium secondary battery of Example 1 was changed from LiPF ₆ to LiBF ₄ or LiClO ₄ to prepare two types of lithium secondary batteries. A lithium secondary battery of Example 1A having an electrolyte of LiBF ₄ and a lithium secondary battery of Example 1B having an electrolyte of LiClO ₄ are used.

Similar to the case of Experiment 1, 28 lithium secondary batteries of each of the above three types were connected in series to form three sets of assembled batteries. The battery case of each set of lithium secondary batteries on the highest potential side and the lowest potential side is
Grounded assuming the use of an actual battery pack. Then, each assembled battery was fully charged, and a load was connected to discharge. At the start of this discharge, in order to simulate leakage of the non-aqueous electrolyte solution, the same non-aqueous electrolyte solution as the one housed in the battery case is placed in the gasket part (position B in FIG. 1) on the positive electrode side, which is the highest potential side. Was dropped to form a bridge of the non-aqueous electrolyte between the nut 33 and the battery case 20. In this way, discharge of each assembled battery was continued.

In the assembled battery composed of the lithium secondary battery of Example 1B, after a while, sparks were generated from the portion where the nonaqueous electrolytic solution was dropped, and the battery temperature rose. In addition, in the battery pack including the lithium secondary battery of Example 1, no spark was observed, but some gas was generated from the portion where the non-aqueous electrolyte was dropped. The battery temperature also rose. On the other hand, in the assembled battery including the lithium secondary battery of Example 1A, neither spark nor gas was generated, and the battery temperature did not rise.

As a reference example, in the lithium secondary battery of Example 1A, a lithium secondary battery was manufactured by changing only the material of the nut 33 on the positive electrode side. That is, the nut 33 on the positive electrode side was formed of a stainless steel (SUS304) material instead of an aluminum alloy material, and other than that, a battery was manufactured in the same manner as the lithium secondary battery of Example 1A. The manufactured lithium secondary battery is used as the lithium secondary battery of Comparative Example 1A. Then, in the same manner as above, the assembled battery was constructed, the non-aqueous electrolyte was dropped, and the discharge was continued. Then, after a while, the generation of sparks was observed in the portion where the non-aqueous electrolyte was dropped. In addition, gas was generated and the battery temperature rose.

From the results of these experiments, the electrolyte was
It was found that by setting F ₄ , generation of gas and increase in battery temperature were suppressed, and generation of sparks was effectively prevented. That is, it was proved that the non-aqueous electrolyte battery of the present invention in which the electrolyte was LiBF ₄ had higher safety when the non-aqueous electrolyte leaked.

<Experiment 5> In the same manner as in Experiment 1 above, charge assembly was performed.
An experiment was conducted to construct a pond and confirm the occurrence of sparks.
The non-aqueous electrolyte battery used in this experiment is the same as that of the second embodiment.
There are two types of thium secondary batteries that differ only in the electrolyte.
It is a lithium secondary battery. Specifically, the Lichi of Example 2
The electrolyte that constitutes the non-aqueous electrolyte in the um secondary battery,
LiPF ₆To LiBF_FourOr LiCl_FourChange to
Two types of lithium secondary batteries were produced. Electrolyte LiB
F_FourAnd a lithium secondary battery of Example 2A,
Decomposition LiClO_FourIs the lithium of Example 2B
Use a secondary battery.

As in the case of Experiment 1, 28 lithium secondary batteries of each of the above two types were connected in series to form two sets of assembled batteries. The battery case of each set of lithium secondary batteries on the highest potential side and the lowest potential side is
Grounded assuming the use of an actual battery pack. Each assembled battery was fully charged, and a load was connected to discharge. At the start of this discharge, in order to simulate leakage of the non-aqueous electrolyte solution, the same non-aqueous electrolyte solution as the one housed in the battery case is placed in the gasket part (position B in FIG. 1) on the positive electrode side, which is the highest potential side. Was dropped to form a bridge of the non-aqueous electrolyte between the nut 33 and the battery case 20. In this way, discharge of each assembled battery was continued.

In the assembled battery composed of the lithium secondary battery of Example 2B, after a while, sparks were generated from the portion where the nonaqueous electrolytic solution was dropped, and the battery temperature rose. On the other hand, in the assembled battery composed of the lithium secondary battery of Example 2A, neither spark nor gas was generated, and the battery temperature did not rise.

From the results of this experiment, the electrolyte was LiBF ₄
It was found that, by setting the above, the generation of gas and the rise in battery temperature are suppressed, and the generation of sparks is effectively prevented. That is, it was proved that the non-aqueous electrolyte battery of the present invention in which the electrolyte was LiBF ₄ had higher safety when the non-aqueous electrolyte leaked.

<Experiment 6> The experiment described here is a current-carrying experiment in a non-aqueous electrolyte, which was conducted to investigate the extent of spark generation by various electrolytes. Two electrode plates (opposing area: 4 cm ² ) made of an aluminum alloy (A1050) material were used, and a PTFE sheet having a thickness of 1 mm was sandwiched between them to form an electrode assembly. This electrode body 1
It was placed in a 00 mL beaker and 10 mL of a non-aqueous electrolyte was injected to immerse the electrode body. The non-aqueous electrolyte is a mixed solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 3: 7, and various electrolytes are dissolved at a concentration of 1M. Then, a power source was connected to each electrode plate of the electrode body, and a constant voltage energization experiment in which a DC voltage of 100 V was applied for 30 minutes between both electrodes was carried out 5 times to examine the occurrence of sparks and the presence or absence of energization. As a result of this experiment, Table 2 below shows the composition of the electrolyte, the degree of spark generation, and the presence or absence of energization. In Table 2, the extent of sparks is indicated by a circle when no sparks have occurred five times, a triangle when at least one spark has occurred, and a cross when all five sparks have occurred. It shows with. When the current value is less than 0.05 A, it is indicated by a circle to indicate whether or not to energize the power source.
When it exceeds 5 A and 0.4 A or less, it is indicated by a triangle, and when it exceeds 0.4 A, it is indicated by a cross.

[0063]

[Table 2]

As can be seen from Table 2 above, the degree of spark generation largely depends on the composition of the electrolyte. In particular, it depends on the content ratio of LiBF _{4 in} the electrolyte. That is,
When the electrolyte consists of LiBF ₄ only (# 61),
No sparks occurred and no current flowed. Also, depending on the kind of other lithium salt to be mixed with LiBF _4, when the electrolyte contains LiBF ₄ it is seen that the generation of the spark is suppressed. In particular, Li
It can be seen that the effect of suppressing the generation of sparks is high when the content ratio of BF ₄ is 25 mol% or more. In addition, LiBF ₄
When the content ratio of was 25 mol% or more, almost no current flowed.

According to this experiment, LiBF ₄ was used as the electrolyte.
It has been proved that by using, the generation of sparks and the energization at the time of leakage of the non-aqueous electrolyte can be effectively suppressed, and a highly safe non-aqueous electrolyte battery can be constructed.

<Experiment 7> A unipolar evaluation test by a potential scanning method was performed to evaluate the anodic polarization characteristics of the aluminum alloy materials due to the difference in the electrolyte composition. The unipolar evaluation test was performed under the following conditions. As an electrode, an electrode plate having an area of 4 cm ² formed of an aluminum alloy (A1070) material was used. As a counter electrode, stainless steel (SU
S304) An electrode plate made of the material was used, and metal Li was used as the reference electrode. Then, using a three-electrode type beaker cell, the above electrodes were arranged, and 10 mL of a non-aqueous electrolyte was injected. The scanning speed was 2 mV / s. The non-aqueous electrolytic solution is a mixed solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 3: 7, and three types of electrolytes having different compositions are dissolved at a concentration of 1M. As a result of the unipolar evaluation test, an anodic polarization curve showing the relationship between the potential and the current density was obtained. The obtained anodic polarization curve is shown in FIG.

From FIG. 4, it is understood that in the case of the electrolyte containing LiBF ₄ , it is difficult for the current to flow even if the potential is raised, and the electrode made of the aluminum alloy material maintains the passive state up to about 10V. In particular, in the case of the electrolyte composed only of LiBF ₄ , almost no current flowed. On the other hand, in the case of the electrolyte containing only LiClO ₄ without LiBF ₄ , active dissolution of the electrode started when the potential reached 4.3 V. From this, it was confirmed that when the electrolyte containing LiBF ₄ was used, the passive state of the aluminum alloy material was stably maintained and almost no current flowed.

<Experiment 8> In the same manner as in Experiment 7, the unipolar evaluation test by the potential scanning method was conducted to evaluate the anodic polarization characteristics of various materials when LiBF ₄ was used as the electrolyte. The unipolar evaluation test was performed in the same manner as in Experiment 7 except that electrodes made of various materials were used as electrodes and only LiBF ₄ was used as the electrolyte. As a result of the unipolar evaluation test, the material of the electrode and the stability of the passive state are shown in Table 3 below. In Table 3, the stability of the passive state is 0-10V.
In the potential range, the case where the current density was less than 0.1 mA / cm ² in ○ mark, indicated by the × mark the case of active dissolved becomes 0.1 mA / cm ² or more.

[0069]

[Table 3]

As can be seen from Table 3, the passive state of the aluminum alloy material is stable regardless of the type of aluminum alloy material. On the other hand, the passive state of Cu, Pb, and stainless (SUS304) materials was not stable, and all materials were active and dissolved when the potential was raised. FIG. 5 shows the anodic polarization curve of each material obtained by the unipolar evaluation test. Note that FIG. 5 shows A1070 as an example of the aluminum alloy material.

From FIG. 5, it can be seen that the electrode made of A1070 hardly passes a current even when the potential is raised and maintains the passive state up to around 10V. On the other hand, C
The electrode composed of u and Pb was active dissolved at a potential of around 4V. The electrode made of SUS304 started active dissolution when the potential became 6V. From this, it was confirmed that when the electrolyte made of LiBF ₄ was used, the passivation film of the aluminum alloy material was stably maintained and the current hardly flowed. That is, the external terminal and its fixing member, and further, the battery case is formed of an aluminum alloy material,
It has been found that the use of the electrolyte containing LiBF ₄ makes it possible to effectively suppress the generation of sparks even when the nonaqueous electrolytic solution leaks, and to form a highly safe nonaqueous electrolytic cell.

[0072]

According to the present invention, a non-aqueous electrolyte battery having a structure having a metal battery case, an external terminal insulated from the metal battery case, and a fixing member for fixing the external terminal is provided. The fixing member is made of an aluminum alloy material and the fixing member is made of an aluminum alloy material or an electrically insulating substance. With such a configuration, in the non-aqueous electrolyte battery of the present invention, even when the non-aqueous electrolyte leaks to the portion to form a bridge, the above-mentioned active radicals are generated by ionization of the transition metal. It is less promoted, the dissociation of the organic solvent is suppressed, and the spark is prevented or suppressed. Furthermore, by using the electrolyte containing LiBF ₄ , even if the nonaqueous electrolytic solution leaks, the current hardly flows and the temperature rise in the leaked part becomes small.
That is, evaporation of the non-aqueous electrolyte solution, generation of combustible gas due to decomposition of the non-aqueous electrolyte solution, and the like are suppressed, and as a result, generation of sparks is effectively suppressed. From the above, the non-aqueous electrolyte battery of the present invention is a non-aqueous electrolyte battery in which high safety is ensured even if the non-aqueous electrolyte leaks.

[Brief description of drawings]

FIG. 1 shows a cross section of a cylindrical lithium secondary battery which is an embodiment of a non-aqueous electrolyte battery of the present invention.

FIG. 2 shows the appearance of the rectangular lithium secondary battery manufactured in Experiment 1.

FIG. 3 shows how a lithium secondary battery is connected in Experiment 1.

FIG. 4 shows anodic polarization curves of aluminum alloy materials according to different electrolyte compositions.

FIG. 5 shows anodic polarization curves of various materials when LiBF ₄ is used as an electrolyte.

[Explanation of symbols]

1: Lithium secondary battery (non-aqueous electrolyte battery) 10: Electrode body 20: Battery case 21: Exterior can 22: Positive side cover plate 23: Negative electrode side cover plate 30: Positive terminal 40: Negative terminal 30b, 40b: External terminal part (external terminal) 32, 42: Washer (fixing member) 33, 43: Nut (fixing member)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 10/40 H01M 10/40 AZ (72) Inventor Hioki Tatsumi Nagakute-cho, Aichi-gun, Aichi Prefecture Toyota Central Research Institute Co., Ltd. at 41 Yokochi (72) Inventor Hiroshi Arakawa 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F Term (reference) 5H011 AA13 CC06 5H022 AA09 CC01 EE04 KK08 5H029 AJ12 AK03 AL06 AM03 AM05 AM07 BJ02 BJ14 BJ27 CJ07 DJ02 DJ05 EJ01 HJ01

Claims (6)

[Claims] 1. A non-aqueous electrolyte battery in which a positive electrode and a negative electrode are housed together with a non-aqueous electrolyte in a battery case made of metal, wherein at least the positive electrode side is insulated from the battery case in the battery case. An external terminal having an attached at least exposed portion formed of an aluminum alloy, and a fixing formed by fixing the external terminal to the battery case and at least an exposed portion formed of a material selected from an aluminum alloy and an electrically insulating substance. A non-aqueous electrolyte battery having a terminal structure including a member. 2. The non-aqueous electrolyte battery according to claim 1, wherein both the positive electrode side and the negative electrode side have the terminal structure. 3. The non-aqueous electrolyte battery according to claim 1, wherein the battery case is made of an aluminum alloy. 4. The non-aqueous electrolyte battery according to claim 1, wherein the aluminum alloy does not contain Cu as a main alloying element. 5. The non-aqueous electrolyte battery according to claim 1, wherein the non-aqueous electrolyte is an electrolyte dissolved in an organic solvent, and the electrolyte contains LiBF ₄ . 6. The non-aqueous electrolyte battery according to claim 5, wherein the content of LiBF _{4 in} the electrolyte is 20 mol% or more based on 100 mol% of the entire electrolyte.