Patent Application
20140127541
The present invention relates to a non-aqueous electrolyte type secondary battery whose battery container includes an electrode winding group formed by winding a strip-shaped positive electrode and a stripe-shaped negative electrode with a strip-shaped separator through which lithium ions can pass interposed between the electrodes.
The strip-shaped positive electrode is formed by applying to an electric collector a positive-electrode active material capable of discharging and accommodating lithium ions by charge and discharge The strip-shaped negative electrode is formed by applying to an electric collector a negative electrode active material capable of accommodating and discharging lithium ions by charge and discharge.
A lithium ion secondary battery (hereinafter, a lithium ion battery) which utilizes storage and discharge of lithium ions in a charge and discharge reaction is widely expected as a power source for portable electronic apparatuses such as a cell phone and a laptop, a power source for time-of-disaster auxiliary, and a power source for mobile objects such as an automobile and a two-wheel vehicle for the following reasons. The lithium ion battery obtains a larger energy density than energy density of the conventional zinc battery or nickel-cadmium battery; since lithium contributing to the charge and discharge reaction is hardly precipitated as metal lithium on an electrode, the possibility that metal lithium drops off from the electrode to be deactivated is low, and for this reason, the lithium ion battery has a superiority in the reproducibility of a capacity when the charge and discharge are repeated; and for the same reason, stable charge-discharge characteristics can be obtained.
In this lithium ion battery, when thermal runaway is caused due to the reasons including overcharge and short-circuit, an inner pressure of the battery rises sharply due to cracked gas of an electrolyte and an electrode, or vapor of the electrolyte. Since the lithium ion battery having an extremely large inner pressure is ruptured by shocks from outside to scatter the contents around, care should be taken when handling the battery.
Here, a battery can lid is generally provided with a current cutoff mechanism which is actuated with a predetermined inner pressure, like the one, for example, described in a patent literary document 1. By the actuation of the current cutoff mechanism, a current is forcibly cut off to forcibly stop a chemical reaction within the battery, thereby preventing rupture or ignition of the battery.
However, as will be described below, there are problems in the lithium ion battery described above.
When the current cutoff mechanism is actuated, there will be no electrical contact between the electrode winding body and the can lid. The means to know the battery voltage will be lost thereby. This is a problem from the viewpoint of managing the battery state.
While the forced cutoff of current can prevent the further charge by the current cutoff mechanism for the chemical reaction within the battery, such a battery after the current cutoff mechanism has been actuated becomes high in dangerousness because the battery breaks down in a state more overcharged than a normal range of use of the battery. This is a problem from the viewpoint of securing the battery safety.
To solve these problems, a method of knowing the battery voltage and carrying out the discharge even after the current cutoff mechanism is actuated has been proposed.
For example, a method of interposing a high-resistance member portion which is substantially an insulating member between a current cutoff valve and an inner sealing plate electrically contacting a terminal plate is proposed in patent literary document 2. According to this method, after the current cutoff the measurement of a battery voltage through the high-resistance member portion can be carried out as well as the discharge.
A method of disposing a current cutoff mechanism and a diode in parallel between an inside of a cover or the cover itself and an electrode winding body is proposed in a patent literary document 3. This method utilizes the characteristics in which the diode can cause a current to flow only in one direction. Thus, the diode is installed in such a way that the current can be caused to flow only in a discharge direction of the battery, whereby a configuration is realized in which after the current cutoff mechanism has been actuated, the charge cannot be carried out, but the discharge can be carried out.
Patent literary document 1: JP-H02-112151-A
Patent literary document 2: JP-2006-147180-A
Patent literary document 3: JP-2004-273139-A
When the measures as described above are considered, there is still something to improve. That is to say, with the method of introducing the high-resistance member as described in the patent literary document 2, there is a drawback that the quick discharge cannot be carried out because the discharge of this method is carried out through the high-resistance member With the method of introducing the diode as described in the patent literary document 3, there is a drawback that the reliability is poor because failure in the diode cannot be detected from outside.
The current cutoff is also caused by the breakage of the electric collector tab in addition to the actuation of the inner pressure sensitive current cutoff mechanism. With those methods, the cause of the current cutoff of the battery can be made clear only after the battery is scrapped. Afterwards general users will not load the lithium ion battery that has undergone the current cutoff to the apparatus to use the battery. The cause of the current cutoff does not matter to the general users therefore. However, for battery manufacturers, the manufacturers preferably are able to figure out which of the causes has contributed to the current cutoff in consideration of the possibility of the battery reutilization, and the feedback for the battery development.
In the light of the foregoing, the present invention provides a cylindrical secondary battery and a battery system that make it possible to perform measurement of a battery voltage, and discharge, and yet whether an inner pressure sensitive current cutoff mechanism is actuated or not can be detected even after a battery inner pressure rises to actuate a current cutoff mechanism. The present invention also provides a battery system that is constructed by incorporating the cylindrical secondary battery.
According to one viewpoint of the present invention, there is provided a cylindrical secondary battery having a pressure sensitive cleavage portion (pressure mechanism A) and a pressure sensitive current cutoff mechanism (pressure mechanism B) in a can lid, the cylindrical secondary battery being characterized in that: the can lid has at least two metal portion A and metal portion B insulated from each other and exposed from a battery inner side to a battery outer side; the metal portion A is electrically connected to an electrode winding body; and the metal portion B is not electrically connected to the electrode winding body before cleavage of the pressure mechanism A, and is electrically connected to the electrode winding body when the pressure mechanism A is cleaved. Also provided is a battery system constructed by incorporating the cylindrical secondary battery.
Specifically, there are provided the cylindrical secondary battery characterized by having a current path A and a current path B within the battery, and the battery system constructed by connecting a discharging element such as a resistive element and a secondary battery to the cylindrical secondary battery.
The current path A is a current path through which the metal portion A and the electrode winding body are linked to each other and which is used in normal charge and discharge. The current path A also electrically contacts the electrode winding body before the pressure mechanism B is actuated, and does not electrically connect to the electrode winding body after the pressure mechanism B is actuated. The current path B is a current path through which the metal portion B and the electrode winding body are linked to each other and which is not used in the normal charge and discharge. The current path B does not electrically contact the electrode winding body before the pressure mechanism A is actuated, and electrically connects to the electrode winding body after the pressure mechanism A is actuated.
In addition, the battery of the present invention is characterized in that the pressure mechanism A is cleaved and the current path B is opened before the actuation of the pressure mechanism B. Therefore, the battery voltage can be detected in the current path B after the current cutoff is detected in the battery, which enables to detect whether the inner pressure sensitive current cutoff mechanism is actuated or not.
Even after the pressure sensitive current cutoff valve is actuated, the measurement of the battery voltage, and discharge can be carried out. The present invention also enables to detect whether the pressure sensitive current cutoff mechanism is actuated or not.
Although the best mode for carrying out the invention will be described hereinafter based on specific embodiments, the present invention is by no means limited thereto. In addition, figures in the embodiment are schematic figures and do not guarantee the precision in information including positional relationship system and sizes in the figures.
A cylindrical secondary battery and a battery system according to the present invention will now be described.
Since a core of the present invention lies in a can lid structure, the can lid structure will now be described especially in detail.
A can lid, as shown in a cross-sectional view of
In the first step, a second inner pressure sensing plate 3 was laminated under a top cap 4 with the inner frame 1 and a packing 2 made of polypropylene in-between. The inner frame 1 was swaged to be stabilized, thereby obtaining the inner frame structure 5.
Second, the inner frame structure 5, a ring-shaped packing 7 made of polypropyrene, and a first inner pressure sensing plate 8 were laminated in this order with the outer frame 6 and a packing 29 made of polyprophylene in-between. The outer frame 6 was swaged to be stabilized, thereby obtaining a can lid 9.
In the next step, to obtain electrical contact between the first inner pressure sensing plate 8 and the second inner pressure sensing plate 3, both of them were subjected to laser welding by using a metallic lead. The welding was carried out only at one point so that a welding point was cut by reversing a reverse portion 13 of the second inner pressure sensing plate 3.
Here, any hole is not present in the first inner pressure sensing plate 8, and for this reason, a space 10 and a space 11 are separated from each other with the first inner pressure sensing plate 8 in-between.
When a cleavage pressure (P1) of a cleavage portion 12 of the first inner pressure sensing plate 8 of the can lid 9 thus obtained, and a reverse pressure (P2) of the reverse portion 13 of the second inner pressure sensing plate 3 were measured, P1 and P2 were both 0.9 Mpa. Here, comparing P1 and P2 with a conventional can lid structure, although P2 corresponds to a pressure at which the current cutoff mechanism is actuated, no pressure corresponding to P1. A gas releasing mechanism for releasing as at a higher pressure than the reverse pressure (P2) may be provided on the second inner pressure sensing plate 3, as insurance for avoiding the rupture of the battery when the battery gets into a situation in which the rise of the battery inner pressure does not stop even after the current cutoff mechanism is actuated due to some sort of trouble.
A 0.3-millimeter-thick aluminum was used for the inner frame 1 and the outer frame 6, and a 0.1-millimeter-thick aluminum was used for the first inner pressure sensing plate 8 and the second inner pressure sensing plate 3. In addition, a cut 14 of the cleavage portion 12 of the first inner pressure sensing plate 8 was provided by press working. A 0.3-millimeter-thick aluminum with a cold-rolled steel strip being nickel-plated thereof was used for a top cap 4.
In the press working for the first inner pressure sensing plate 8, a shape of the cut 14 needs to be adjusted in such a way that the cleavage portion 12 is folded to a side facing the inner frame 1 and thus the cleavage portion 12 comes in electric contact with the inner frame 1 when the cleavage portion 12 is cleaved. As shown in
A portion 16 exposed from the packing is preferably provided in the inner frame 1 as shown in
LiNi0.33Mn0.33Co0.33O2 as a positive-electrode active material, powdered carbon as a conducting agent, and a polyvinyliden fluoride (PVDF) as a binding agent were measured at a weight ratio of 85:10:5, and a suitable amount of N-methyl-pyrrolidone (NMP) was added as a solvent thereto. The solution was mulled for 30 min by using a mulling mechanism, thereby obtaining positive-electrode slurry. The resulting positive-electrode slurry was applied to both surfaces of an aluminum foil (having a thickness of 20 μm and a width of 56 mm), thereby obtaining a positive-electrode sheet 18. Natural graphite, powdered carbon, and PVDF were used as a negative-electrode active material, the conducting agent, and the binding agent, respectively, and a suitable amount of NMP was added as the solvent thereto. The solution was mulled at a weight ratio of the negative-electrode active material:the conducting agent:and the binding agent=90:5:5 by the same manufacturing method as the manufacturing method for the positive electrode, thereby obtaining negative-electrode slurry. The resulting negative-electrode slurry was applied to both surfaces of a copper foil (thickness of 10 μm, width of 57 mm), thereby obtaining a negative-electrode sheet 19.
After the positive-electrode electric collector lead portion 20 made of aluminum, and a negative-electrode electric collector lead portion 21 made of nickel were welded to the positive-electrode sheet 18 and the negative-electrode sheet 19, respectively, both of the electrodes were subjected to roll molding at 13 t to 14 t by using a pressing machine. Then, the resulting members were subjected to vacuum drying at 120° C. for 3 hours. After the drying, the positive-electrode sheet 18 and the negative-electrode sheet 19 were wound in the manner as shown in
After the electrode winding body 24 was inserted into a cylindrical can 25, the negative-electrode electric collector lead portion 21 was resistance-welded to bottom of a can. Next, to obtain the electrical contact between the first inner pressure sensing plate 8, and the positive-electrode electric collector lead portion 20 extending from the electrode winding body 24, both of them were subjected to the resistance-welding. Also, after an electrolyte (created by dissolving LiPF6 in a liquid solution in which ethylene carbonate (EC):1,2-dimethoxy ethane (EMC)=1:3 so as to obtain a concentration of 1M of LiPF6) was injected, the can lid 9 was sealed by swaging the can, thereby obtaining a cylindrical secondary battery 26 according to the present invention.
Here, a dotted line 27 with an arrow (current path A27) linking the electrode winding body—the electric collector tab—the first inner pressure sensing plate—the welded portion—the second inner pressure sensing plate—the top cap shown in
For a cleavage pressure (P1) of the cleavage portion 12 of the first inner pressure sensing plate 8, and an actuation (reverse) pressure (P2) of the second inner pressure sensing plate 3, although not being definite, a relationship of P1≧P2 preferably holds. This relationship holds, whereby the reverse portion 13 of the second inner pressure sensing plate 3 can be reversed instantly after the cleavage of the cleavage portion 12 of the first inner pressure sensing plate 8. The opening of the current path B28 due to the cleavage of the cleavage portion 12 of the first inner pressure sensing plate 8 shown in
In a case where the discharging element is incorporated in the current path B28, thereby constructing the battery system, P1≧P2 is set, which results in that the flowing of the current from an external load connected to the current path A27 to the discharging element into the current path B28 can be kept to the minimum, and the discharging element can be simplified. For example, the discharging element can also be composed of only a simple resistive element or a secondary battery. In addition to the resistive element or the secondary battery, a miniature bulb and an acoustic sound alarm can be mounted to disseminate that the current is flowing into the charging element when the battery is overcharged.
Such simplification of the discharging element cannot be realized with conventional compositions. That is to say, with the conventional configurations, in addition to the current path through the top cap 4 (hereinafter, a current path C. Making comparison with this embodiment, it corresponds to the current path A), the current path through a cap frame (hereinafter, a current path D. Making comparison with this embodiment, it corresponds to the current path B) is present. Since the current path D electrically contacts the electrode winding body 24 from the normal phase, if the simple resistive element or the secondary battery is connected to the current path D, the load applied to the current path C would spread to the current path D as well. If the discharging element were connected to the current path D with a conventional composition, the battery system composition would be complicated with. a large number of control circuits needed. The reasons are it is required to monitor if the current path C is not in an overcharged state in addition to providing a circuit with a mechanism that cuts an influence of the load applied to the current path C in a normal phase. Further, discharging, for example, must be carried out in the current path D when the current path C is in an overcharged state.
After the current cutoff is detected in the current path A27, the voltage of the current path B28 is observed by using the exposed portion 16 of the inner frame 1 of the can lid 9, making it possible to perform the measurement of the battery voltage, and the discharge. By the observation of voltage of the current path B, presence or absence of the actuation of the inner pressure sensitive current cutoff mechanism can be detected. cl DESCRIPTION OF REFERENCE NUMERALS
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/003554 | 6/22/2011 | WO | 00 | 12/18/2013 |
