JP3175928B2 - Rechargeable battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery using a non-aqueous electrolyte.

[0002]

2. Description of the Related Art In recent years, remarkable progress in electronic technology has enabled electronic devices to be reduced in size and weight one after another. Along with this, there is a demand for batteries as portable information terminals to be increasingly smaller, lighter and have higher energy density. Further, in consideration of recent environmental problems, particularly air pollution, electric vehicles (EV) and hybrid electric vehicles (HEV) that do not emit carbon monoxide or nitrogen compounds have attracted attention, and large-capacity secondary batteries and There is a demand for a secondary battery capable of extracting a large current.

Conventionally, the life of a lithium-ion secondary battery for use in a portable terminal is considered to be 3 when considered as its cycle life.
Charge and discharge of 00 to 500 cycles are generally considered as a guide. Therefore, it is generally considered that a capacity of about 50 to 60% of the initial capacity can be maintained after 300 to 500 cycles. On the other hand, in recent years, lithium ion secondary batteries for use in EVs and HEVs are considered to require thousands to hundreds of thousands of cycles in view of the durability of a vehicle to be mounted.

[0004]

However, when the conventional battery design method for a portable terminal is applied to an EV or HEV battery, the following problems occur. That is, in order to make maximum use of the high weight energy density of the lithium ion secondary battery, it is necessary for the battery for a portable terminal to be reduced to the minimum battery weight that satisfies the above-mentioned battery life. Particularly in recent mobile phones, reducing the weight of the telephone is a major issue, so that all battery components are kept to the minimum necessary weight. However, it has been found that when a long-term charge / discharge cycle for EV or HEV is performed using a battery manufactured based on the above-described battery design standard for a portable terminal, the battery life is reached before required thousands to hundreds of thousands of cycles. . Investigation into the cause revealed that the most influential was the lack of electrolyte.

In general, the amount of the electrolyte has a lower limit, and if the amount is lower than the lower limit, the impedance between the electrodes increases, and the electrolyte cannot be used as a battery. On the other hand, if a sufficient amount is injected with a margin from the lower limit, it leads to an increase in weight, volume and cost. For the above reasons, the amount of electrolyte is kept to a necessary minimum in a battery for a portable terminal having a large weight limit.
Also, batteries for mobile terminals are required to improve not only the weight energy density but also the volume energy density.Therefore, the ratio of battery elements to the internal volume of the battery can is large. Has an upper limit, and it is practically impossible to inject an electrolytic solution higher than the upper limit. Therefore, the present invention has been proposed in view of such conventional circumstances, and an object of the present invention is to provide a battery that can be driven without running out of electrolyte even in charging and discharging of thousands to hundreds of thousands of cycles. I do.

[0006]

The present invention relates to a non-aqueous electrolyte secondary battery in which a battery element comprising a wound body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound via a separator is accommodated in a battery can. Only the separator is wound at the end of the wound body other than the part where the positive electrode and the negative electrode of the battery element face each other, and the separator pore volume at the end of the winding is 10 to 50 of the total pore volume of the electrode group in which the positive electrode and the negative electrode face each other. % Secondary battery. In the above secondary battery, the active material is for doping and undoping lithium ions.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The non-aqueous electrolyte secondary battery of the present invention
In a non-aqueous electrolyte secondary battery in which a battery element in which a strip-shaped positive electrode and a strip-shaped negative electrode are spirally wound via a separator is accommodated in a battery can, other than a portion where the electrode active material of the spiral-shaped battery element is provided Is formed with an electrolyte holding portion. The electrolytic solution holding portion is characterized in that a portion including only the separator is formed at the rearmost portion of the wound body of the battery element, and the electrolytic solution holding portion is provided.

The non-aqueous electrolyte secondary battery of the present invention uses a spiral battery element in which a strip-shaped positive electrode and a strip-shaped negative electrode are stacked with a separator interposed therebetween, and the electrode stack is wound many times. And especially, long-term cycle of non-aqueous electrolyte secondary battery,
For example, a porous body for holding an electrolyte is provided inside the spiral battery element or outside the battery element so that the electrolyte does not become insufficient even in tens of thousands to hundreds of thousands of cycles. No attempt has been made to dispose such a filling in order to replenish the electrolyte in such a spiral battery element.

Usually, in the case of a lithium ion secondary battery using a lithium transition metal composite oxide such as lithium cobalt oxide or lithium manganate for the positive electrode and a carbon material capable of doping / dedoping lithium ions for the negative electrode,
The consumption of the electrolyte during the charge / discharge cycle does not appear as a remarkable difference in the battery performance in several tens to several hundreds of cycles. However, actually, it is considered that it is gradually consumed by decomposition in the battery reaction.

As a result, in the case of performing a long-term cycle exceeding several thousand cycles, a shortage of the electrolyte is apparently caused only by holding the electrolyte in the spiral battery element alone. Therefore, if a porous body capable of replenishing the electrolyte held in the spiral battery element is disposed inside or outside the battery element, a battery that does not deteriorate in capacity even in a long cycle can be obtained.

The electrolyte holding section can be realized by a method in which a porous substance for holding an electrolyte is present on the outer peripheral portion of the wound body. The electrolytic solution holding portion is formed by forming a portion of only the separator by independently winding the separator located on the outer peripheral portion of the wound body.

In the present invention, the porosity of the filler is a value obtained by dividing the sum of the void volumes of the positive electrode, the negative electrode and the separator by the total volume of the positive electrode, the negative electrode and the separator. For example, when expressing the void volume of the positive electrode, Equation 1 is obtained.

The void volume of the positive electrode = (positive electrode winding length × positive electrode width × positive electrode active material thickness) − [(total positive electrode weight per unit area of electrode × positive electrode winding length × positive electrode width) × ((positive electrode active material Content / positive material active material density) + (auxiliary material content / auxiliary material density))] Formula 1 Formula 1 represents the space volume in the positive electrode, and actually corresponds to the portion impregnated with the electrolyte. The porosity is obtained by dividing the formula 1 by the positive electrode volume (positive electrode winding length × positive electrode width × positive electrode active material thickness). The negative electrode is also represented by the same formula as the positive electrode, and actually corresponds to a portion impregnated with the electrolytic solution.

[0014] The separator itself has a porosity in the material itself, and the porosity volume is used for holding the electrolytic solution and for the passage of lithium ions. The above is the calculation method in design, but the actual numerical value is verified by a volume measurement method using helium gas filling using a pycnometer. As a result, it has been confirmed that there is almost no difference between the calculation of the pore volume and the actual volume measurement.

When the porosity of the filler is 10 to 50% of the volume of the pores including the separator at the portion where the positive electrode and the negative electrode face each other in the wound battery element, it is less than 10%. The effect is not remarkable. Similarly, in the case of a general method of manufacturing a wound battery element, a small amount of a separator alone is present in the portion where the positive electrode and the negative electrode do not face each other, but there is no effect of replenishing the electrolyte. Conversely 50
% Is not practical because a significant difference in long-term cycle and the like cannot be confirmed and the occupation ratio of the filler in the battery can is large, so that the battery capacity is significantly reduced.

Further, there is usually a space inside the battery can other than the wound battery element. For example, a cylindrical battery has a columnar space at the center of a wound battery element, and a rectangular battery has a space at a corner inside the space between batteries. In the present invention, these spaces are not considered as electrolyte holding portions.
This is because the electrolyte is blown out by the usual method of injecting the solution under reduced pressure, and it is impossible to control and maintain the amount of the electrolyte in these spaces.

The present invention will be described below with reference to the drawings. FIG. 1 is an exploded perspective view showing a secondary battery according to one embodiment of the present invention, and is a view showing a state where a lid of the battery is removed. In a secondary battery 1 of the present invention, a battery can 2 as a container is formed in a cylindrical shape, and a battery element 3 having a similar shape is accommodated in the inside thereof. The battery element 3 includes strip-shaped positive and negative electrodes 4 and 5 formed by applying an active material and strip-shaped separators 6 and 7, and the electrodes 4 and 5 are stacked with the separators 6 and 7 interposed therebetween. It is wound by. Electrode leads 8 and 9 are attached to one end of each of the electrodes 4 and 5, and an electrolytic solution holding unit 10 composed of a separator wound alone is arranged on the outer peripheral portion of the battery element. The separator is fixed.

As described above, the secondary battery 1 of the present embodiment has a cylindrical outer shape, so that the extra space in the battery can has only a central portion in cross-sectional shape. In the case of the present embodiment, repeated charging and discharging over a long period of several thousand to several tens of thousands of cycles is possible because the winding layer of the separator alone exists on the outer peripheral portion of the battery element, so that it can be used for holding the electrolytic solution. However, good performance can be stably exhibited without lowering the capacity.

[0019]

[0020]

[0021]

[0022]

[0023]

In the secondary battery according to the present invention, a belt-shaped positive electrode mainly composed of lithium manganate and a lithium ion-doped lithium ion are used.
A band-shaped negative electrode composed mainly of a undoped carbon material and a battery element in which a separator alone is arranged at the rear portion of a battery element wound with a separator interposed therebetween, and a battery having a sufficient amount of electrolyte is used. A battery with less capacity deterioration can be obtained even in a long cycle.

[0024]

The present invention will be described below with reference to examples. Example 1 A negative electrode mixture obtained by mixing 66.6 parts by weight of a mesophase-based carbon material powder and 7.4 parts by weight of polyvinylidene fluoride (PVDF) as a binder was mixed with 26 parts by weight of N-methyl 2-pyrrolidone as a solvent. To prepare a negative electrode mixture slurry. The obtained negative electrode mixture slurry was applied to both sides of a 15 μm-thick strip-shaped copper foil, dried, and then compression-formed to produce a strip-shaped negative electrode. The band-shaped negative electrode had the same mixture thickness of 50 μm on both sides after molding, had a width of 57 mm,
The length was 650 mm. Then, a flat plate made of nickel having a thickness of 0.1 mm and a width of 3 mm was welded to one end of the negative electrode to form a negative electrode lead.

Further, lithium carbonate and manganese dioxide are mixed and calcined in air at a temperature of 780 ° C. for 12 hours to produce LiM
n ₂ O ₄ was obtained. This LiMn ₂ O ₄ was used as a positive electrode active material, and 50.6 parts by weight of this was used as a conductive agent.
75 parts by weight, polyvinylidene fluoride 1.6 as a binder
5 parts by weight were mixed to prepare a positive electrode mixture. Then, this positive electrode mixture was dispersed in 45 parts by weight of N-methyl 2-pyrrolidone to obtain a positive electrode mixture slurry.

The obtained slurry of the positive electrode mixture was coated with a thickness of 25 μm.
After uniformly applying and drying both sides of the m-shaped strip-shaped aluminum foil, it was compression-formed to prepare a strip-shaped positive electrode.
The thickness of the mixture on both sides of the electrode on the positive electrode side is 60
μm, the width is 55.5 mm and the length is 600 mm
And Then, a flat plate made of aluminum having a thickness of 0.1 mm and a width of 3 mm was welded to one end of the positive electrode manufactured as described above to form a positive electrode lead.

The strip-like positive and negative electrodes prepared as described above are connected to a negative electrode, a first separator, and a positive electrode through a separator made of a microporous polypropylene film having a thickness of 25 μm and a width of 60 mm. , The second separator, and the like, and one end of the electrode laminate was fixed to a core having a circular cross section and wound 20 times.

After the lamination of the positive and negative electrodes is completed, the first and second separators are further wound 10 times to form all the holes in the portion where the positive and negative electrodes and the two-layer separator face each other and are laminated. An electrolytic solution holding portion corresponding to 20% (corresponding to 0.6 ml) of the corresponding volume was formed.

After the laminate was wound around the core in this manner, the final end of the separator located at the outermost periphery was fixed to the roll with an adhesive tape having a width of 15 mm. Then, the battery core was manufactured by extracting the core from the wound body.

Next, the positive electrode lead was welded to the battery can, the negative electrode lead was welded to the battery lid, and 30 parts by weight of ethylene carbonate and 70 parts by weight of diethyl carbonate were mixed from the electrolyte injection portion. In the solvent,
An electrolyte solution in which LiPF ₆ was dissolved at a rate of 1 mol / l was injected, and the battery cover and the battery can were fixed by caulking to maintain the secrecy in the battery. The amount of electrolyte is positive and negative electrodes and 2
In addition to 20% of the volume corresponding to the total pores in the portion where the layer separators face each other and stacked, an electrolyte corresponding to the pore volume in the filled portion was added. Through the above steps, the diameter is 18 mm and the height is 65
mm non-aqueous electrolyte secondary battery was manufactured.

The above is the case of 20% of the volume corresponding to the total porosity of the portion where the positive and negative electrodes and the two-layer separator are stacked facing each other. A total of 10 secondary batteries were manufactured in each of the battery elements having the ratio changed from 10% to 80% of the total porosity of the laminated portion of the positive and negative electrodes and the two-layer separator for each 10%. The charge / discharge cycle was repeated up to 10,000 times after performing constant current charging for 1 hour under the conditions of an upper limit voltage of 4.2 V and a charging current of 1.2 A, and then performing discharging under the conditions of a voltage of 3.0 V and 1 C. The maintenance rate was examined.

FIG. 2 shows this initial capacitance distribution.
FIG. 3 shows the distribution of the capacity retention ratio after 000 cycles. As is apparent from these drawings, when the volume of pores in the electrolyte holding portion is 10% or more of the total volume of pores in the laminated portion of the positive and negative electrodes and the two-layer separator, the capacity retention rate is extremely reduced. Less. This is because the electrolyte solution is held in a volume corresponding to the electrolyte solution holding portion to compensate for the consumption of the electrolyte solution.
However, when the amount of the electrolyte holding portion exceeds 50%, the volume of the separator occupying the battery can becomes large, so that the initial capacity starts to decrease remarkably. For this reason, it is not practical to secure a certain or more battery capacity.

From this, it has been found that arranging the electrolyte holding portion in the battery element is effective in preventing the capacity of the secondary battery from decreasing in thousands to tens of thousands of cycles. In other words, the secondary battery according to the present embodiment has the filling portion 1 that can hold the electrolyte in addition to the positive and negative electrodes facing each other as described above.
Since 0 is arranged, even if charge / discharge is repeated several thousands to tens of thousands of times, the electrolyte can be stably provided without shortage of electrolyte solution. In addition, as a method of manufacturing the secondary battery of the embodiment, the battery element having the wound structure is formed by the same method as in the related art, and the electrolytic solution holding portion is arranged in the forming process, so that the structure can be simplified. Can be realized.

[0034]

As described above, the secondary battery of the present invention is provided with an electrolytic solution holding portion other than the portion where the positive electrode and the negative electrode of the battery element face each other, and holds the electrolytic solution. Of the battery capacity can be prevented.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a secondary battery as an embodiment of a battery to which the present invention is applied.

FIG. 2 is a diagram illustrating an initial capacity distribution of a battery according to an example.

FIG. 3 is a diagram illustrating a distribution of a capacity retention rate after 10,000 cycles.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Secondary battery, 2 ... Battery can, 3 ... Battery element, 4, 5 ... Electrode, 6, 7 ... Separator, 8, 9 ... Electrode lead, 10 ...
Electrolyte holding part, 11 ... adhesive tape

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 2/14-2/18 H01M 10/04 H01M 10/40

Claims (2)

(57) [Claims] In a non-aqueous electrolyte secondary battery in which a battery element formed of a wound body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound via a separator is accommodated in a battery can, the positive electrode and the negative electrode of the battery element face each other. The separator is wound only at the end of the winding body other than the part to be wound, and the separator pore volume at the end of the winding is 10 to 50% of the total pore volume of the electrode group in which the positive electrode and the negative electrode face each other. Rechargeable battery. 2. The secondary battery according to claim 1, wherein the active material is used for doping and undoping lithium ions.