Patent Description:
A secondary battery such as a lithium ion secondary battery has such a structure that an electrode body including a positive electrode plate and a negative electrode plate is housed together with an electrolytic solution in a battery case.

Patent Document <NUM> discloses a rectangular secondary battery configured such that a wound electrode body is housed in a rectangular battery case. Ends (electrode foil) of positive and negative electrode plates protruding from both end portions of the electrode body in a winding axis direction are each connected to external terminals fixed to a sealing plate through current collectors. The sealing plate is provided with a gas discharge valve, and when a gas pressure exceeds a predetermined value, the gas discharge valve is ruptured to release gas generated in the battery to the outside of the battery.

<CIT> relates to a sealed battery lid having a thin wall portion and an insulating sealing member for fixing an electrode terminal by insert molding, which prevents cleavage of the thin wall portion during manufacturing.

<CIT> relates to a battery module with a cap assembly structure having a good process stability when manufacturing the battery module.

A joint method by ultrasonic welding has been known as the method for joining the ends of the positive and negative electrode plates and the current collectors. Ultrasonic welding is performed in such a manner that vibration energy of ultrasonic waves is applied to joint surfaces while the end of the positive or negative electrode plate and the current collector are sandwiched by a hom and an anvil.

It is necessary to reduce a battery intemal resistance in a high-power battery in order to obtain sufficient output characteristics. For this reason, the resistance also needs to be reduced for the current collectors forming current paths from the positive and negative electrode plates to the external terminals. Thus, the thickness of the current collector needs to be increased.

If the thickness of the current collector is increased, in a case where the ends of the positive and negative electrode plates and the current collectors are joined by ultrasonic welding, the vibration energy needs to be high. The current collector is connected to the external terminal fixed to the sealing plate. Thus, ultrasonic vibration applied to the current collector propagates to the gas discharge valve provided at the sealing plate by way of the external terminal and the sealing plate. As a result, there is a probability that when the vibration energy upon ultrasonic welding has increased, the gas discharge valve is ruptured by the ultrasonic vibration having propagated to the gas discharge valve by way of the current collector.

The invention is as set out in the independent claims, further aspects of the invention are outlined in the dependent claims. Embodiments that do not fall within the scope of the claims do not describe part of the invention.

A rectangular secondary battery according to the present invention includes an electrode body including a positive electrode plate and a negative electrode plate, a rectangular battery case having an opening and housing the electrode body, a sealing plate sealing the opening, a current collector extending on an end side of the sealing plate in a longitudinal direction thereof and joined, by ultrasonic welding, to an end of the positive electrode plate or the negative electrode plate, and an external terminal provided outside the sealing plate and connected to the current collector. The sealing plate has a gas discharge valve ruptured when the internal gas pressure of the battery case has reached a predetermined value or greater, and a thin portion formed between the external terminal and the gas discharge valve and formed thicker than the gas discharge valve, wherein when the smallest distance between any two points of the gas discharge valve and the external terminal is H and the distance between the gas discharge valve and the thin portion is h, h/H ≥ <NUM> is satisfied.

The method for manufacturing a rectangular secondary battery according to the present invention is the method for manufacturing a rectangular secondary battery configured such that an electrode body including a positive electrode plate and a negative electrode plate is housed in a rectangular battery case. The method includes a step of attaching an external terminal and a current collector connected to the external terminal to a sealing plate for sealing an opening of the battery case, a step of joining, by ultrasonic welding, the current collector extending on an end side of the sealing plate in a longitudinal direction thereof to an end of the positive electrode plate or the negative electrode plate, and a step of housing the electrode body in the battery case and sealing the opening of the battery case with the sealing plate. The sealing plate has a gas discharge valve ruptured when an intemal gas pressure of the battery case has reached a predetermined value or greater, and a thin portion formed between the external terminal and the gas discharge valve and formed thicker than the gas discharge valve, wherein when the smallest distance between any two points of the gas discharge valve and the external terminal is H and the distance between the gas discharge valve and the thin portion is h, h/H ≥ <NUM> is satisfied.

According to the present invention, the rectangular secondary battery configured so that vibration propagating to the gas discharge valve by way of the current collectors can be absorbed when the ends of the positive and negative electrode plates and the current collectors are joined by ultrasonic welding.

Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiment below. Moreover, changes can be made as necessary without departing from a scope in which advantageous effects of the present disclosure are produced.

<FIG> is views schematically showing a configuration of a rectangular secondary battery in one embodiment of the present disclosure, <FIG> is a plan view, <FIG> is a sectional view along an Ib-Ib line of <FIG> is a sectional view along an Ic-Ic line of <FIG>.

As shown in <FIG>, a rectangular secondary battery <NUM> in the present embodiment is configured such that an electrode body <NUM> as a power generation element is housed together with an electrolytic solution in a rectangular battery case <NUM>. An opening of the battery case <NUM> is sealed with a sealing plate <NUM>.

The electrode body <NUM> has such a structure that a positive electrode plate and a negative electrode plate are stacked or wound with a separator interposed therebetween. The positive electrode plate is configured such that a positive electrode active material layer is provided on surfaces of a positive electrode core. The negative electrode plate is configured such that a negative electrode active material layer is provided on surfaces of a negative electrode core.

Each of the positive and negative electrode plates has, at end portions in a longitudinal direction of the sealing plate <NUM>, ends <NUM>, <NUM> formed with no active material layer. The ends <NUM>, <NUM> of the positive and negative electrode plates are, in a bundled state, joined to positive and negative electrode current collectors <NUM>, <NUM> by ultrasonic welding.

The materials of the positive and negative electrode current collectors <NUM>, <NUM> are not particularly limited, but are preferably the same materials as those of the positive and negative electrode cores. With this configuration, the ends <NUM>, <NUM> of the positive and negative electrode plates and the current collectors <NUM>, <NUM> can be easily welded by ultrasonic welding. For example, in the case of a lithium ion secondary battery, the positive electrode current collector <NUM> is preferably made of aluminum or aluminum alloy, and the negative electrode current collector <NUM> is preferably made of copper or copper alloy.

The positive and negative electrode current collectors <NUM>, <NUM> are each connected to positive and negative electrode external terminals <NUM>, <NUM> provided outside the sealing plate <NUM>. The external terminals <NUM>, <NUM> are each insulated from the sealing plate <NUM> by insulating members <NUM>, <NUM>.

The sealing plate <NUM> is provided with a gas discharge valve <NUM>. The gas discharge valve <NUM> is ruptured when the internal gas pressure of the battery case <NUM> has increased to a predetermined value or greater, thereby releasing gas from the battery. The gas discharge valve <NUM> includes a thin portion thinner than other portions of the sealing plate <NUM>.

In the present embodiment, the sealing plate <NUM> has a thin portion <NUM>, <NUM> formed between each of the positive and negative electrode external terminals <NUM>, <NUM> and the gas discharge valve <NUM> and formed thicker than the gas discharge valve <NUM>. The thickness of the thin portion <NUM>, <NUM> is set to such a size that the thin portion <NUM>, <NUM> is not ruptured in advance of the gas discharge valve <NUM> when the internal gas pressure of the battery case <NUM> has increased to the predetermined value or greater.

As described above, it is necessary to reduce a battery internal resistance in a high-power battery in order to obtain sufficient output characteristics. For this reason, the current collectors <NUM>, <NUM> forming current paths from the positive and negative electrode plates to the external terminals <NUM>, <NUM> also need to be increased in thickness in order to reduce the resistance. As a result, as the thicknesses of the current collector <NUM>, <NUM> increase, vibration energy when the ends <NUM>, <NUM> of the positive and negative electrode plates and the current collectors <NUM>, <NUM> are welded by ultrasonic welding increases.

Meanwhile, when the ends <NUM>, <NUM> of the positive and negative electrode plates and the current collectors <NUM>, <NUM> are welded by ultrasonic welding, ultrasonic vibration applied to the current collectors <NUM>, <NUM> propagates to the gas discharge valve <NUM> provided at the sealing plate <NUM> by way of the external terminals <NUM>, <NUM> and the sealing plate <NUM>. As a result, there is a probability that when the vibration energy upon ultrasonic welding has increased, the gas discharge valve <NUM> is ruptured due to the ultrasonic vibration having propagated to the gas discharge valve <NUM> by way of the current collectors <NUM>, <NUM>.

In the present embodiment, the thin portion <NUM>, <NUM> is provided between the external terminal <NUM>, <NUM> and the gas discharge valve <NUM>, and therefore, the ultrasonic vibration propagating from the external terminal <NUM>, <NUM> to the gas discharge valve <NUM> by way of the sealing plate <NUM> is absorbed by the thin portion <NUM>, <NUM>.

The ultrasonic vibration having propagated to the external terminals <NUM>, <NUM> from the current collectors <NUM>, <NUM> propagates to the gas discharge valve <NUM> by way of the sealing plate <NUM>. Since the thin portions <NUM>, <NUM> provided at the sealing plate <NUM> are thinner than other portions of the sealing plate <NUM>, the thin portions <NUM>, <NUM> have a lower flexural rigidity than those of other portions of the sealing plate <NUM>. A transverse wave of the ultrasonic vibration is a torsional wave, and therefore, the ultrasonic vibration is attenuated at a portion with a low flexural rigidity, i.e., the thin portions <NUM>, <NUM>, in the course of propagating in the sealing plate <NUM>. As a result, the attenuated ultrasonic vibration propagates to the gas discharge valve <NUM>, and therefore, excessive stress due to the ultrasonic vibration is not applied to the gas discharge valve <NUM>. As a result, rupture of the gas discharge valve <NUM> due to the ultrasonic vibration having propagated to the gas discharge valve <NUM> by way of the current collectors <NUM>, <NUM> can be prevented.

<FIG> are views showing analysis results, which are obtained by simulation, of the amount of deformation of the sealing plate <NUM> when the ultrasonic vibration propagates in the sealing plate <NUM>.

<FIG> is a view in a case where no thin portion is provided at the sealing plate <NUM>, and <FIG> two-dimensionally shows, by the shade of color, displacement of the sealing plate <NUM> in a thickness direction thereof when the ultrasonic vibration is applied to the negative electrode current collector <NUM>.

<FIG> is a view in a case where the thin portions <NUM>, <NUM> are provided at the sealing plate <NUM>, and <FIG> two-dimensionally shows, by the shade of color, the displacement of the sealing plate <NUM> in the thickness direction thereof when the ultrasonic vibration is applied to the negative electrode current collector <NUM>. Note that the thin portion <NUM>, <NUM> was arranged substantially in the middle between the gas discharge valve <NUM> and the external terminal <NUM>, <NUM>.

The simulation was conducted using a direct frequency response analysis by means of an analysis model of a fine element method solver (ANSYS). The sealing plate <NUM> was made of aluminum (A1050) so as to have a thickness of <NUM>, a width of <NUM>, and a length of <NUM>.

The thin portion <NUM> was formed in an oval shape so as to have a thickness of <NUM>, a width of <NUM>, and a length of <NUM>. The frequency of the ultrasonic vibration applied to the negative electrode current collector <NUM> was <NUM>, and the amplitude of the ultrasonic vibration was <NUM>.

<FIG> is a graph showing a relationship between the displacement of the sealing plate <NUM> in the thickness direction thereof and a distance from a center portion of the sealing plate <NUM> when the ultrasonic vibration is applied to the negative electrode current collector <NUM>. The displacement in the thickness direction as described herein indicates displacement along the center axis J of the sealing plate <NUM>.

In <FIG>, a curved line indicated by an arrow P shows a graph in a case where the thin portion <NUM> is not provided, and a curved line indicated by an arrow Q shows a graph in a case where the thin portion <NUM> is provided.

<FIG> shows that the displacement of the sealing plate <NUM> in the thickness direction thereof greatly decreases in a region A between the center portion of the sealing plate <NUM> and the thin portion <NUM> in the case (the curved line Q) of providing the thin portion <NUM> than in the case (the curved line P) of not providing the thin portion <NUM>. That is, it shows that the thin portion <NUM> is provided at the sealing plate <NUM> so that the ultrasonic vibration propagating from the external terminal <NUM> to the gas discharge valve <NUM> by way of the sealing plate <NUM> can be absorbed by the thin portion <NUM>.

In the present embodiment, an effect of absorbing the ultrasonic vibration by the thin portions <NUM>, <NUM> depends on the degree of decline in the flexural rigidity of the sealing plate <NUM>. Thus, in order to obtain a sufficient absorption effect, at least t ≤ <NUM>. 8T is preferable and t ≤ <NUM>. 5T is more preferable when the thickness of the sealing plate <NUM> is T and the thickness of the thin portion <NUM>, <NUM> is t.

If the thickness of the thin portion <NUM>, <NUM> is too small, the sealing plate <NUM> is distorted at the thin portion <NUM>, <NUM> when the internal gas pressure of the battery has increased. As a result, there is a probability that the battery case <NUM> is deformed. For this reason, the thickness t of the thin portion <NUM>, <NUM> is preferably <NUM>. Note that the thickness of the gas discharge valve <NUM> is normally set to equal to or less than <NUM>/<NUM> of the thickness of the sealing plate <NUM>, and therefore, if the thickness t of the thin portion <NUM>, <NUM> is set to <NUM>. 2T, the thin portion <NUM>, <NUM> is not ruptured in advance of the gas discharge valve <NUM>.

Note that in a case where the thickness of the thin portion <NUM>, <NUM> is not uniform, the thickness of a thinnest portion is defined as the thickness of the thin portion <NUM>, <NUM>. In a case where the thickness of the gas discharge valve <NUM> is not uniform, the thickness of a thinnest portion is defined as the thickness of the gas discharge valve <NUM>.

In the present embodiment, the shape of the thin portion <NUM>, <NUM> is not particularly limited. <FIG> is views showing one example of the thin portion <NUM>, <NUM>, <FIG> is a plan view, and <FIG> is a sectional view along a Vb-Vb line of <FIG>. The thin portion <NUM>, <NUM> is an oval extending in a width direction of the sealing plate <NUM>. The thin portion <NUM>, <NUM> in such a shape can be formed by pressing, for example. The thin portion <NUM>, <NUM> may be divided in the width direction of the sealing plate <NUM>. Alternatively, multiple thin portions <NUM>, <NUM> may be provided between the external terminal <NUM>, <NUM> and the gas discharge valve <NUM>.

As shown in <FIG>, the length W of the thin portion <NUM> (only the negative electrode side thin portion is shown) in the width direction of the sealing plate <NUM> is preferably longer than the length L of the gas discharge valve <NUM> in the width direction of the sealing plate <NUM>. The thin portion <NUM> wider than the gas discharge valve <NUM> is provided before the gas discharge valve <NUM>, and therefore, functions as a bulwark against the ultrasonic vibration propagating to the gas discharge valve <NUM>. Thus, the ultrasonic vibration propagating to the gas discharge valve <NUM> can be more effectively attenuated.

<FIG> is a view and a graph showing results, which are obtained by simulation, of a change in the maximum stress value on the gas discharge valve <NUM> when the position of the thin portion <NUM>, <NUM> provided between the external terminal <NUM>, <NUM> and the gas discharge valve <NUM> has changed.

<FIG> is a view showing the arrangement position of the thin portion <NUM> when a distance between an end portion of the gas discharge valve <NUM> and an end portion of the insulating member <NUM> is H' and a distance between the end portion of the gas discharge valve <NUM> and the thin portion <NUM> is h. In this case, the thin portion <NUM> is arranged between the end portion of the gas discharge valve <NUM> and the end portion of the insulating member <NUM>.

<FIG> is a graph showing a change in the maximum stress value on the gas discharge valve <NUM> when h/H' has changed. Note that simulation conditions were the same as those shown in <FIG>. Moreover, a line indicated by an arrow S indicates the maximum stress value in a case where the thin portion <NUM> is not provided.

<FIG> shows that within a range in which h/H ≥ <NUM> is satisfied, the maximum stress value on the gas discharge valve <NUM> decreases as compared to the maximum stress value in the case of not providing the thin portion <NUM>.

On the other hand, if the position of the thin portion <NUM> is too close to the gas discharge valve <NUM> (h/H < <NUM>), the gas discharge valve <NUM> originally having a low flexural rigidity and the thin portion <NUM> purposefully provided as a portion having a low flexural rigidity become similar to each other as a portion having a low flexural rigidity, and for this reason, an effect produced by the thin portion <NUM> is reduced.

If the position of the thin portion <NUM> is too close to the insulating member <NUM> (h/H' > <NUM>), it is difficult to form the thin portion <NUM> at the sealing plate <NUM> by, e.g., pressing.

Thus, when the distance between the gas discharge valve <NUM> and the insulating member <NUM>, <NUM> is H' and the distance between the gas discharge valve <NUM> and the thin portion <NUM>, <NUM> is h, the thin portion <NUM>, <NUM> is preferably arranged at a position satisfying h/H' ≥ <NUM>. Considering formability of the thin portion <NUM>, <NUM>, h/H' ≤ <NUM> is preferably satisfied.

Note that the above-described simulation was conducted taking the distance between the end portion of the gas discharge valve <NUM> and the end portion of the insulating member <NUM> as H', but results similar to those of <FIG> were obtained taking a distance between the end portion of the gas discharge valve <NUM> and an end portion of the external terminal <NUM> as H as shown in <FIG>.

Next, the method for manufacturing the rectangular secondary battery according to the present embodiment will be described with reference to <FIG>.

First, as shown in <FIG>, the external terminals <NUM>, <NUM> and the current collectors <NUM>, <NUM> connected to the external terminals <NUM>, <NUM> are attached to the sealing plate <NUM> for sealing the opening of the battery case <NUM>. The sealing plate <NUM> is formed with the gas discharge valve <NUM> and the thin portions <NUM>, <NUM> in advance.

Next, as shown in <FIG>, the electrode body <NUM> is arranged such a position that the ends <NUM>, <NUM> of the positive and negative electrode plates overlap with the current collectors <NUM>, <NUM>, and the ends <NUM>, <NUM> of the positive and negative electrode plates and the current collectors <NUM>, <NUM> are ultrasonic-welded at welding portions <NUM>, <NUM> by a normal method. At this point, since the sealing plate <NUM> is provided with the thin portions <NUM>, <NUM>, the ultrasonic vibration propagating from the current collectors <NUM>, <NUM> to the gas discharge valve <NUM> by way of the external terminals <NUM>, <NUM> and the sealing plate <NUM> is absorbed by the thin portions <NUM>, <NUM>. As a result, rupture of the gas discharge valve <NUM> when the ends <NUM>, <NUM> of the positive and negative electrode plates and the current collectors <NUM>, <NUM> are welded by ultrasonic welding can be prevented.

Finally, as shown in <FIG>, the electrode body <NUM> attached to the sealing plate <NUM> is housed in the rectangular battery case <NUM>, and thereafter, the sealing plate <NUM> is welded to an opening edge of the battery case <NUM>. In this manner, the rectangular secondary battery is completed.

The present disclosure has been described above with reference to the preferable embodiment, but such description is not limitative and various modifications can be made, needless to say.

Claim 1:
A rectangular secondary battery (<NUM>) comprising:
an electrode body (<NUM>) including a positive electrode plate (<NUM>) and a negative electrode plate (<NUM>);
a rectangular battery case (<NUM>) having an opening and housing the electrode body (<NUM>);
a sealing plate (<NUM>) sealing the opening;
a current collector (<NUM>, <NUM>) extending on an end side of the sealing plate (<NUM>) in a longitudinal direction thereof and joined, by ultrasonic welding, to an end of the positive electrode plate (<NUM>) or the negative electrode plate (<NUM>); and
an external terminal (<NUM>, <NUM>) provided outside the sealing plate (<NUM>) and connected to the current collector (<NUM>, <NUM>),
wherein the sealing plate (<NUM>) has
a gas discharge valve (<NUM>) ruptured when an internal gas pressure of the battery case (<NUM>) has reached a predetermined value or greater, and
a thin portion (<NUM>, <NUM>) formed between the external terminal (<NUM>, <NUM>) and the gas discharge valve (<NUM>) and formed thicker than the gas discharge valve (<NUM>);
wherein, when the smallest distance between any two points of the gas discharge valve (<NUM>) and the external terminal (<NUM>, <NUM>) is H and the distance between the gas discharge valve (<NUM>) and the thin portion (<NUM>, <NUM>) is h, h/H ≥ <NUM> is satisfied.