This application claims priority to a Chinese patent application entitled “Cylindrical Lithium Ion Secondary Batteries” filed on Sep. 1, 2003, having a Chinese Patent Application No. 03140377.8; this Chinese application is incorporated herein by reference. This application further claims priority to a Chinese patent application entitled “Stacked Lithium Ion Secondary Batteries” filed on Sep. 1, 2003, having a Chinese Patent Application No. 03140376.X; this Chinese application is incorporated herein by reference. This application further claims priority to a Chinese patent application entitled “Lithium Ion Secondary Batteries” filed on Oct. 28, 2003, having a Chinese Patent Application No. 2003101119664; this Chinese application is incorporated herein by reference.
The present invention relates to a type of cylindrical lithium ion secondary battery, in particular, to a type of highly safe cylindrical lithium ion secondary battery.
Along with the rapid development of the electronic industry and communication industry, people's demand for power for the electronic devices is getting higher and higher. Cylindrical lithium ion secondary battery being a high capacity power source is being used in a variety of areas, especially for laptop batteries. Its electrical characteristics, especially its safety characteristics, are becoming highly important.
Currently, the combined characteristics of the cylindrical lithium ion secondary battery are good. With respect to its safety characteristics, the potential for internal or external short circuiting is the greatest concern, with internal short-circuiting being the greater concern of the two. In practical applications, due to unavoidable shaking or dropping of the battery and thereby easily causing internal short-circuiting within the battery, the battery is required to possess highly safe and flexible characteristics. In the design and improvement of cylindrical lithium ion secondary battery, the most common anti-explosion design is when there is short-circuiting, a safety switch opens and the battery quickly discharges to prevent explosion. For example, Chinese Patent No. CN2556798 describes a cylindrical lithium ion secondary battery having an anti-explosion insert to prevent, due to battery internal or external short-circuiting, the battery temperature and pressure rapidly rising causing the battery to explode. This type of methods, although it can effectively prevent battery explosion causing harm to electronic devices and the user, once the anti-explosion insert is broken, the electrolyte can leak. Due to the breakage, the battery is rendered useless and the corresponding electronic device can no longer function.
Therefore, people begin to study how to raise the safety characteristics when the battery internally short-circuits, and fundamentally control the breakage of the battery. However, as of now, cylindrical lithium ion secondary battery uses a single electrode group formed by a positive electrode, a negative electrode, and a separator all rolled into a cylindrically-shape and uses it as the battery core. This type of battery core has the following problems: when there is an internal short in certain point or certain area, the entire battery becomes short-circuited, where the battery internally generates a large current and instantly discharges. The internal temperature will rapidly increase, increasing the internal pressure, rendering the entire battery useless. During this time, there is no guarantee to its safety-worthiness and the electronic device cannot continue to function.
Due to the popularity of the cylindrical lithium ion secondary battery in the market place, especially as the primary battery for laptop computers, the above problems must be conquered.
An object of the present invention is to provide a type of cylindrical lithium ion secondary battery, where when there is an internal short, the battery voltage does not change and can be continued to be used safely and reliably.
Another object of the present invention is to provide a battery having one of the positive or negative electrodes formed by a number of smaller electrodes where said smaller electrodes are individually wrapped with separation material in order to eliminate any separation areas between the smaller electrodes.
Still another object of the present invention is to provide a battery and manufacturing method thereof where each of the electrodes having a conducting strip for current conduction and yet melts during a short-circuit condition.
Briefly, in the presently preferred embodiment, a type of cylindrical lithium ion secondary battery, having a positive electrode, a negative electrode, and a separator forming a cylindrical electrode group, along with electrolyte all encased in a battery shell and sealed by a battery cover, is disclosed. Here, one of the positive electrode(s) or negative electrode(s) is a belt-shaped electrode, while the other electrode(s) is formed by at least two smaller pieces of electrodes. After stacking the positive electrode(s), the separator, and the negative electrode(s), the stack is rolled to form a cylindrical electrode group and the smaller pieces of electrodes are in mutually disconnected and segregated state. Each of the positive and negative electrodes has a conducting strip for conduction of electrical current with the battery shell or the battery cover.
An advantage of the present invention is that it provides a type of cylindrical lithium ion secondary battery, where when there is an internal short, the battery voltage does not change and can be continued to be used safely and reliably.
Another advantage of the present invention is that it provides a battery having one of the positive or negative electrodes formed by a number of smaller electrodes where said smaller electrodes are individually wrapped with separation material in order to eliminate any separation areas between the smaller electrodes.
Still advantage of the present invention is that it provides a battery and manufacturing method thereof where each of the electrodes having a conducting strip for current conduction and yet melts during a short-circuit condition.
The present invention is further described by the figures in conjunction with the description of the embodiments.
a-5b illustrate the derivation of the concept where a gap is created when a rectangular shaped electrode is rolled into a cylindrical shaped electrode group.
a-6c illustrate the different shapes of the electrodes in order to minimize the separation area between two smaller electrodes.
In the present invention, in a presently preferred embodiment, the cylindrical-shaped lithium ion secondary battery has one of the positive or negative electrodes as a belt-shaped electrode and the other electrode formed by at least two smaller electrodes. After arranging and stacking with the separator, it is rolled to form a cylindrical shaped electrode group and the smaller electrodes are mutually non-conductive, with the positive and negative electrodes' conducting strips connected to the battery cover or battery shell. This structure is equivalent to a battery formed by many smaller electrical sources connected together. When one of the smaller electrical source short-circuits, a large current is generated instantaneously, and other smaller electrical sources of the smaller electrodes simultaneously supply current to it, where the current passing through the conducting strip of the electrode instantaneously increases causing it to melt and break. In the manner, it controls and stops the supply and release of electricity from other electrical sources to this short-circuited source. The energy of the short-circuited small electrical source is depleted, while other electrodes providing electrical sources can continue to function. Fundamentally the battery has not changed except for the lowered battery capacity and decreased recharge time, but the battery can continued to be used.
In practical applications, the preferred number of smaller electrodes forming the electrode group is 2-6 pieces. It can selectively vary depending on the size of the battery but not more than 6 pieces, because too many small electrodes will affect battery capacity and complicates the industrial manufacturing process.
Furthermore, in the described cylindrical-shaped electrode group, the belt-shaped electrode is placed externally to the smaller pieces of electrodes.
The advantages of the cylindrical lithium ion secondary battery of the present invention includes: through the cylindrically-shaped electrode group, one of the positive or negative electrodes being a belt-shaped electrode and the other electrode formed by at least two smaller electrodes; when the battery short-circuits internally at a certain location, the damage is limited to the electrode at that location, depleting the capacity of the electrode at that location, and resulting in minimal changes to the battery where the battery may continued to be used in a safe and reliable manner.
The cylindrical lithium ion secondary battery of the present invention (referring to
Both the positive and negative electrodes have conducting strips for current conduction. Each of the three smaller electrodes 1 forming the positive electrode has a conducting strip 7 connecting with the battery cover 6, and the negative electrode 2 has a conducting strip 8 connecting to the battery shell.
In the manufacturing of the battery, the separator 3 wraps the negative electrode 2 along its long edge and it is placed on the bottom; the three smaller pieces forming the positive electrode 1 is placed in order on the top, and a separation area 9 is created (as illustrated in
The present invention is further described by the embodiments and testing results below.
Embodiment 1
Manufacturing model 1865, labeled capacity being 2100 mAh, a cylindrical lithium ion secondary battery, the manufacturing process is described below:
The making of the positive electrode: mixing 100 units by weight of LiCoO2 powder, 7 units by weight of crystalline-shaped carbon as conducting paste, and 7 units by weight of PVDF as sticky paste; diluting in sufficient solution of N-methyl pyrrolidone to form a paste; smearing said compound paste on both sides of a 20 μm aluminum foil to obtain positive electrodes having the dimension of 212×55.5×0.12 mm for a total of three pieces.
The making of the negative electrode: mixing 100 units by weight of man-made carbon powder, 10 units by weight of PTFE as sticky paste; diluting in sufficient amount of ion-free solution to form a paste; evenly smearing said compound paste on both sides of a 10 μm copper foil to obtain negative electrodes having the dimension of 700×570.0×0.14 mm. On a side area not smeared with paste of each positive electrode, a strip-shaped aluminum conducting strip is ultra-sonically welded on; on a side area not smeared with paste of the negative electrode, a belt-shaped copper conducting strip is ultra-sonically welded on; and the conducting strips 7 of the positive electrodes and the conducting strip 8 are illustrated in
The battery shell uses steel shell having 0.3 mm in thickness; a 0.5 mm through hole is prepared at the half height of the round sidewall; and said hole is sealed with tape on the outside.
In accordance with
Comparison Embodiment 1
A cylindrical lithium ion secondary battery, model 1865, has a battery core made using normal method for the manufacturing of single positive electrode plate, single negative electrode plate, and single separator all rolled into a cylindrically-shaped electrode group, labeled capacity being 2100 mAh. Other than its positive electrode is one piece with a conducting strip, it is the same as embodiment 1.
I. Testing of the battery's initial use:
2. testing of the battery's initial capacity: charge the battery to 4.2 v; discharge at the rate of 0.5C until it reaches 3.0V; test the capacity.
II. Battery Internal Short Circuit Test using a Pin: Using a fully charged battery, removing the sealing tape on the 0.5 mm through hole on the external wall, using a 0.3 mm needle for testing internal short circuit to insert into said through hole, holding the inserted depth to: thickness of the steel wall+thickness of the negative electrode+thickness of the separator+0.5 times of the thickness of the positive electrode, i.e.: 0.3+0.14+0.2+0.06=0.7 (mm), creating a short circuit between the negative electrode and outer-most small positive electrode of the battery core of the cylindrical lithium ion secondary battery.
In the needle test, from the instant when the needle is inserted 0.7 mm deep, the following items are tested:
1. Change in temperature of the battery surface: Record of the temperature change of the battery surface within 20 minutes of the battery short-circuiting (see table 2).
2. Change in battery voltage: Record of battery voltage change within 20 minutes of the battery short-circuiting (see table 3). 3. In testing, observe to see if there are signs of leakage, fire or explosion (see table 4).
The above tables 2-3 recorded the corresponding test results, and it is apparent: where there is an internal short-circuiting within a certain area of the cylindrical lithium ion secondary battery of the present invention, the maximum temperature does not exceed 100 degrees, and the battery voltage only changes when there is short-circuiting, but returns to the working voltage of 3.6V, and there is no leakage, explosion or other undesirable conditions, proving the battery can continue to function. In the battery of the comparison embodiment there was leakage after 10.5 minutes, the battery became partly burned, the surface temperature reached 167° C., and the voltage was around 1.4V; the battery became useless and cannot continue to work.
III. Testing after the battery has been short-circuited: 20 minutes after the battery has been needle short-circuited, the battery function is tested. Because the comparison embodiment has already leaked and rendered useless, it cannot be tested. In testing embodiment 1 as follows:
In comparing the characteristics of the battery in its initial use and after short-circuiting (table 5):
As known from table 5, the battery of the comparison embodiment is rendered useless after it short-circuits internally, while the present embodiment after short-circuiting, only the affected the functioning of the positive electrode where the short-circuit occurred, the battery capacity decreased by about one-third of the initial capacity, and the battery internal resistance decreased slightly, but the battery can be continued to be used, reliably and safely.
IV. In dissecting the above-described post-test battery, it is discovered that the conducting strip of the outer-most positive electrode of the battery of the embodiment has melted, while the conducting strips of the other two positive electrodes are fine. Because the battery of the comparison embodiment only has one electrode, the conducting strip has been charred and remains connected.
Preferred Embodiments
In providing several smaller electrodes in order to isolate short-circuiting damaging to one of the smaller electrodes, the trade-off here is that the capacity of the battery would be decreased due to the overall capacity provided by sum of the smaller electrodes would be smaller than the overall capacity provided by a single long, belt-shaped electrode. This is because a separation area is required between the smaller electrodes. In the improved embodiments, the focus here becomes how to maximize the overall capacity of the battery.
In yet another alternative method, the separation area remains but is minimized between the smaller electrodes. From a theoretical perspective, given a rectangular object as illustrated in
In yet another embodiment, referring to
While the present invention has been described with reference to certain preferred embodiments, it is to be understood that the present invention is not to be limited to such specific embodiments. Rather, it is the inventor's contention that the invention be understood and construed in its broadest meaning as reflected by the following claims. Thus, these claims are to be understood as incorporating and not only the preferred embodiment described herein but all those other and further alterations and modifications as would be apparent to those of ordinary skilled in the art.
Number | Date | Country | Kind |
---|---|---|---|
03 1 40377.8 | Sep 2003 | CN | national |
03140376.X | Sep 2003 | CN | national |
2003101119664 | Oct 2003 | CN | national |