Patent Description:
A battery module generally includes secondary batteries arranged sequentially, and each secondary battery is provided with an electrode assembly inside. In the charge process or discharge process, the electrode assembly will expand in an arrange direction of the secondary batteries; expanding forces generated by the electrode assemblies of the secondary batteries will be accumulated in the arrange direction and form an excessive composite force; the composite force presses the secondary batteries, which leads to the secondary battery being unable to work normally and influences the life of the secondary battery. Related technologies are known from <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

From <CIT> there is known a secondary battery, comprising an electrode assembly, a case and a cap assembly; the case having an accommodating cavity, the accommodating cavity having an opening at an end of the case in an axial direction, and the electrode assembly being accommodated in the accommodating cavity; the electrode assembly comprising electrode units; the cap assembly comprising a cap plate and a vent piece, the cap plate being connected with the case and positioned at a side of the electrode assembly in the axial direction; the cap plate being provided with a through-hole, the vent piece being connected with the cap plate and covering the through-hole; the cap plate having a first inner surface at a side close to the electrode assembly, the vent piece having a second inner surface at a side close to the electrode assembly, and a distance between the first inner surface and the electrode assembly being smaller than a distance between the second inner surface and the electrode assembly.

In view of the problem existing in the background, an object of the present invention is to provide a secondary battery, a battery module and an electric vehicle, which can avoid a vent piece rupturing and improve the performance and life of the secondary battery. The present invention is defined in the independent claim.

In order to achieve the above object, the present invention provides a secondary battery, as defined in claim <NUM>, a battery module as defined in claim <NUM> and an electric vehicle as defined in claim <NUM>.

The dependent claims define further embodiments of the invention.

The secondary battery in accordance with some embodiments comprises an electrode assembly, a case and a cap assembly. The case has an accommodating cavity, the accommodating cavity has an opening, and the electrode assembly is accommodated in the accommodating cavity. The electrode assembly comprises electrode units, and the electrode units are stacked in an axial direction of the accommodating cavity. The cap assembly comprises a cap plate and a vent piece, the cap plate is connected with the case and positioned at a side of the electrode assembly in the axial direction. The cap plate is provided with a through-hole, and the vent piece is connected with the cap plate and covers the through-hole. The cap plate has a first inner surface at a side close to the electrode assembly, the vent piece has a second inner surface at a side close to the electrode assembly, and the second inner surface is positioned at a side of the first inner surface away from the electrode assembly.

In some embodiments of the secondary battery, the cap plate is further provided with a first groove, the first groove extends from the first inner surface in a direction away from the electrode assembly, and the first groove is disposed along a periphery of the through-hole. The vent piece is provided in the first groove, and a depth of the first groove is larger than a thickness of the vent piece.

In some embodiments of the secondary battery, the cap plate is further provided with a second groove, the second groove extends from the first inner surface along the direction away from the electrode assembly, and the second groove is disposed along a periphery of the first groove. The depth of the first groove is larger than a depth of the second groove.

In some embodiments of the secondary battery, the depth of the second groove is <NUM>-<NUM>.

In some embodiments of the secondary battery, the first groove and the second groove form a step surface, the step surface is flush with the second inner surface. The vent piece in accordance with some embodiments is welded with a side wall of the first groove by laser.

In some embodiments of the secondary battery, the cap plate is further provided with a third groove, the third groove is provided at a side of the cap plate away from the electrode assembly, and the third groove is disposed along a periphery of the through-hole. The vent piece is provided in the third groove.

In some embodiments of the secondary battery, the second inner surface is parallel to the first inner surface.

The secondary battery in accordance with some embodiments further comprises an insulating member, the insulating member is provided at the side of the cap plate close to the electrode assembly and connected with the cap plate. A first gap is kept between the vent piece and the insulating member.

In some embodiments of the secondary battery, the insulating member has a third inner surface at a side close to the electrode assembly, and a flatness of the third inner surface is smaller than or equal to <NUM>.

In some embodiments of the secondary battery, a second gap is kept between the insulating member and the first inner surface.

In some embodiments of the secondary battery, the electrode unit is a flat structure and has a wide surface and a narrow surface. The wide surface is disposed to face the first inner surface, the second inner surface and the third inner surface in the axial direction, the narrow surface is connected with the wide surface and positioned at an end of the electrode unit in a width direction. The narrow surface in accordance with some embodiments is in the shape of arc.

The battery module in accordance with some embodiments comprises the secondary battery, and the secondary battery is provided as plurality in number and the plurality of secondary batteries are arranged sequentially, an arrange direction of the secondary batteries is perpendicular to the axial direction.

The electric vehicle in accordance with some embodiments comprises the battery module.

The present invention has the following beneficial effects. In the present invention, the electrode units of the secondary battery are arranged in the axial direction, so expansions of the electrode units will be accumulated in the axial direction. In the battery module, the arrange direction of the secondary batteries is perpendicular to the axial direction, so even though the expansion amounts of all the electrode assemblies are accumulated in the arrange direction, it still will not generate an excessive composite force, thereby avoiding the secondary battery being crushed, and ensuring the performance and life of the secondary battery. By providing the second inner surface recessed relative to the first inner surface, when the electrode units expand, it can decrease the probability that the vent piece ruptures under normal gas pressure, reduce safety risk and extend the working life of the secondary battery.

Reference numerals in figures are represented as follows:.

To make the object, technical solutions and advantages of the present invention more apparent, hereinafter the present invention will be further described in detail in combination with the accompanying figures and the embodiments. It should be understood that the specific embodiments described herein are merely used to explain the present invention but are not intended to limit the present invention.

In the description of the present invention, unless otherwise specifically defined and limited, the terms "first", "second" and "third" are only used for illustrative purposes and are not to be construed as expressing or implying a relative importance. The term "plurality" is two or more. Unless otherwise defined or described, the term "connect" should be broadly interpreted, for example, the term "connect" can be "fixedly connect", "detachably connect", "integrally connect", "electrically connect" or "signal connect". The term "connect" also can be "directly connect" or "indirectly connect via a medium". For the persons skilled in the art, the specific meanings of the abovementioned terms in the present invention can be understood according to the specific situation.

In the description of the present invention, it should be understood that spatially relative terms, such as "above", "below" and the like, are described based on orientations illustrated in the figures, but are not intended to limit the embodiments of the present invention.

In the present invention, a battery module in accordance with some embodiments generally includes a secondary battery, an end plate, a side plate and a busbar. The secondary battery is provided as plurality in number and the plurality of secondary batteries are arranged sequentially. The secondary battery of the present invention may be a prismatic lithium-ion battery. An arrange direction of the secondary batteries may be parallel to a width direction Y of each secondary battery. The end plate is provide as two in number and the two end plates are respectively provided at two ends of the secondary batteries in the arrange direction, the side plate is provided as two in number and the two side plates are respectively provided at two sides of the secondary batteries. The end plates and the side plates are welded together to form a rectangular frame. The secondary batteries are fixed to the frame. The busbar connects the secondary batteries together in series, in parallel or in series-parallel.

Referring to <FIG> and <FIG>, the secondary battery in accordance with some embodiments includes an electrode assembly <NUM>, a case <NUM>, a cap assembly <NUM> and a current collecting member <NUM>.

An accommodating cavity <NUM> is formed in the case <NUM> to receive the electrode assembly <NUM> and an electrolyte. An opening is formed at an end of the case <NUM> in an axial direction Z, and the electrode assembly <NUM> is placed into the case <NUM> via the opening. The case <NUM> may be made of conductive metal material, such as aluminum, aluminum alloy or the like. The axial direction Z is parallel to an extending direction of the accommodating cavity <NUM> and perpendicular to a plane in which the opening is located. The battery module in accordance with some embodiments can be used in an electric vehicle; when the cap assembly <NUM> of the secondary battery in the electric vehicle is substantially parallel to the ground, the axial direction Z is parallel to a height direction of the secondary battery, perpendicular to the width direction Y of the secondary battery, a length direction X of the secondary battery and the arrange direction of the secondary batteries.

The electrode assembly <NUM> in accordance with some embodiments includes electrode units <NUM>, and the electrode units <NUM> are stacked in the axial direction Z of the accommodating cavity <NUM>. Referring to <FIG>, each electrode unit <NUM> includes a first electrode plate <NUM>, a second electrode plate <NUM> and a separator <NUM>, and the separator <NUM> separates the first electrode plate <NUM> and the second electrode plate <NUM>. The electrode unit <NUM> can be formed by spirally winding the first electrode plate <NUM>, the second electrode plate <NUM> and the separator <NUM>, and the electrode unit <NUM> is pressed to a flat structure. Alternatively, each electrode unit <NUM> also can be formed by stacking the first electrode plate <NUM>, the second electrode plate <NUM> and the separator <NUM>.

The first electrode plate <NUM> includes an aluminum foil and a positive active material coated on a surface of the aluminum foil, the positive active material includes lithium manganese oxide or lithium iron phosphate. The second electrode plate <NUM> includes a copper foil and a negative active material coated on a surface of the copper foil, the negative active material includes graphite or silicon.

The cap assembly <NUM> in accordance with some embodiments includes a cap plate <NUM>, a vent piece <NUM>, an insulating member <NUM> and an electrode terminal <NUM>.

The cap plate <NUM> is connected with the case <NUM> and covers the opening of the case <NUM>, thereby sealing the electrode assembly <NUM> inside the accommodating cavity <NUM> of the case <NUM>. The insulating member <NUM> is provided at a side of the cap plate <NUM> close to the electrode assembly <NUM>, that is, the insulating member <NUM> is provided between the cap plate <NUM> and the electrode assembly <NUM>; the insulating member <NUM> may be connected with the cap plate <NUM> by thermal melting. The electrode terminal <NUM> is provided to the cap plate <NUM> and protrudes to outside of the cap plate <NUM>. Both of the electrode terminal <NUM> and the current collecting member <NUM> are provided as two in number, one the current collecting member <NUM> connects the first electrode plate <NUM> and one electrode terminal <NUM>, the other current collecting member <NUM> connects the second electrode plate <NUM> and the other electrode terminal <NUM>.

In the charge process or discharge process, each electrode unit <NUM> will expand. In some embodiments, the electrode units <NUM> of the secondary battery are stacked in the axial direction Z, so expansions of the electrode units <NUM> will be accumulated in the axial direction Z. In the width direction Y, the expansions of the electrode units <NUM> is smaller, so the overall expansion amount of the electrode assembly <NUM> in the width direction Y is smaller, correspondingly, an expanding force applied to the case <NUM> by the electrode assembly <NUM> is smaller too.

In the battery module, the arrange direction of the secondary batteries is perpendicular to the axial direction Z, so even though the expansion amounts of all the electrode assemblies <NUM> are accumulated in the arrange direction, it still will not generate an excessive composite force, thereby avoiding the secondary battery being crushed, and ensuring the performance and life of the secondary battery.

In addition, in known technology, two end plates of the battery module need to clamped the secondary batteries; if the composite force generated by the expansions of the secondary batteries is excessive, it may lead to a welding position between the end plate and the side plate fracturing and result in failure of the battery module. In the present invention, the composite force generated by the secondary batteries when expanding is small, thereby avoiding the failure of the battery module.

The cap plate <NUM> is positioned at a side of the electrode assembly <NUM> in the axial direction Z, in other words, the cap plate <NUM> is positioned at an end of the electrode units <NUM> in a stacked direction of the electrode units <NUM>. The cap plate <NUM> is provided with a through-hole <NUM>, the through-hole <NUM> may be positioned at a central region of the cap plate <NUM> in the length direction X. The cap plate <NUM> has a first inner surface <NUM> at a side close to the electrode assembly <NUM>, and the first inner surface <NUM> is a substantially flat surface perpendicular to the axial direction Z.

The vent piece <NUM> is connected with the cap plate <NUM> and covers the through-hole <NUM>. The vent piece <NUM> has a second inner surface <NUM> at a side close to the electrode assembly <NUM>, and the second inner surface <NUM> is substantially parallel to the first inner surface <NUM>.

The vent piece <NUM> has a notch. When the secondary battery suffers short circuit, the electrode assembly <NUM> generates a large amounts of gas, the gas can break through the vent piece <NUM>, thereby timely exhausting the gas to the outside of the secondary battery, avoiding explosion and reducing safety risk.

Referring to <FIG> and <FIG>, in the secondary battery, when the electrode units <NUM> expand, the expansions of the electrode units <NUM> will be accumulated in the axial direction Z, thereby leading to the electrode unit <NUM> of the electrode assembly <NUM> closest to the insulating member <NUM> pressing the insulating member <NUM>. The insulating member <NUM> transfers an expanding force to the first inner surface <NUM> of the cap plate <NUM>, which leads to deformation of the cap plate <NUM>. In known technology, the vent piece <NUM> is mostly provided below the cap plate <NUM>; when the electrode units <NUM> expand, the insulating member <NUM> will press the vent piece <NUM>; the strength of the vent piece <NUM> is small, so the vent piece <NUM> is easy to rupture under the influence of pressure, thereby resulting in safety risk and leading to a failure of secondary battery.

Therefore, preferably, referring to <FIG>, the second inner surface <NUM> is positioned at a side of the first inner surface <NUM> away from the electrode assembly <NUM>, that is, a distance d2 between the first inner surface <NUM> and the electrode assembly <NUM> is smaller than a distance d1 between the second inner surface <NUM> and the electrode assembly <NUM>. In the present invention, the second inner surface <NUM> is recessed relative to the first inner surface <NUM>, so when the electrode units <NUM> expand, the first inner surface <NUM> can block the electrode unit <NUM> and the insulating member <NUM>, avoid the insulating member <NUM> directly pressing the vent piece <NUM>, thereby avoiding the rupture of the vent piece <NUM> under normal gas pressure, reducing safety risk and extending the working life of the secondary battery.

The insulating member <NUM> is provided with exhaust holes below the vent piece <NUM>. When the secondary battery suffers short circuit, the gas can be applied to the vent piece <NUM> via the exhaust holes, thereby breaking through the vent piece <NUM> and exhausting the gas to the outside of the secondary battery.

Referring to <FIG> and <FIG>, the cap plate <NUM> in accordance with some embodiments is further provided with a first groove <NUM>, the first groove <NUM> extends from the first inner surface <NUM> in a direction away from the electrode assembly <NUM>, and the first groove <NUM> is disposed along a periphery of the through-hole <NUM>. The first groove <NUM> is in the shape of annulus. The vent piece <NUM> is provided in the first groove <NUM>, in the axial direction Z, a depth t1 of the first groove <NUM> is larger than a thickness of the vent piece <NUM>. A surface of the vent piece <NUM> away from the electrode assembly <NUM> is attached on an annular bottom wall of the first groove <NUM>, and a periphery of the vent piece <NUM> may be welded with a side wall of the first groove <NUM>.

In the present invention, by providing the first groove <NUM>, a value of the distance d1 is larger than a value of the distance d2, thereby avoiding the vent piece <NUM> rupturing under the influence of the expansion of the electrode assembly <NUM>.

Preferably, the cap plate <NUM> is further provided with a second groove <NUM>, the second groove <NUM> extends from the first inner surface <NUM> along the direction away from the electrode assembly <NUM>, and the second groove <NUM> is disposed along a periphery of the first groove <NUM>. The second groove <NUM> is in the shape of annulus, and a distance d4 between a side wall of the second groove <NUM> and a center axis of the through-hole <NUM> is larger than a distance d3 between the side wall of the first groove <NUM> and the center axis of the through-hole <NUM>.

The depth t1 of the first groove <NUM> is larger than a depth t2 of the second groove <NUM>. By providing the first groove <NUM> and the second groove <NUM>, a step structure is formed in the cap plate <NUM>. When assembling the cap plate <NUM> and the vent piece <NUM>, it puts the vent piece <NUM> into the first groove <NUM> firstly and makes the vent piece <NUM> attached on the bottom wall of the first groove <NUM>, then welds the side wall of the first groove <NUM> and the vent piece <NUM> together. In the present invention, by providing the second groove <NUM>, a junction between the side wall of the first groove <NUM> and the vent piece <NUM> is exposed, so a laser can directly act to the junction, thereby simplifying welding process and improve welding accuracy.

When the electrode units <NUM> expand, the insulating member <NUM> deforms under the influence of the expanding force; when the insulating member <NUM> deforms, it may extend into the second groove <NUM>; if the depth of the second groove <NUM> is too small, the insulating member <NUM> may still press the vent piece <NUM>, which leads to the vent piece <NUM> rupturing, therefore, preferably, the depth of the second groove <NUM> is not less than <NUM>.

If the depth of the second groove <NUM> is too large, the cap plate <NUM> needs to have a larger thickness; the larger the thickness of the cap plate <NUM> is, the greater the strength of the cap plate <NUM> is. When the electrode units <NUM> expand, the cap plate <NUM> will apply a larger reaction force to the electrode unit <NUM>, the reaction force will decrease a gap between the first electrode plate <NUM> and the second electrode plate <NUM>, which leads to the electrolyte being unable to enter into the electrode unit <NUM> and results in lithium precipitation. Therefore, preferably, the depth of the second groove <NUM> is not larger than <NUM>. In conclusion, the depth of the second groove <NUM> is preferably <NUM>-<NUM>.

The first groove <NUM> and the second groove <NUM> form a step surface, the step surface is an annular bottom wall of the second groove <NUM> and is flush with the second inner surface <NUM>; the "flush" is not required to be absolutely flush, and an allowable error is acceptable. When the step surface is flush with the second inner surface <NUM>, the laser directly acts to a junction between the step surface and the second inner surface <NUM>, thereby simplifying welding process and improve welding accuracy.

When the electrode units <NUM> expand, the insulating member <NUM> deforms under the influence of the expanding force; if the insulating member <NUM> contacts the second inner surface <NUM> of the vent piece <NUM>, the insulating member <NUM> is easy to crush the vent piece <NUM>. Therefore, preferably, a first gap is kept between the vent piece <NUM> and the insulating member <NUM>.

Further, in some embodiments, a second gap is kept between the insulating member <NUM> and the first inner surface <NUM>. By providing the second gap, it avoids the cap plate <NUM> limiting the deformation of the insulating member <NUM>, thereby functioning as buffering. In other words, the second gap can decrease the expanding force transferred to the cap plate <NUM> by absorbing the expansion of the electrode assembly <NUM>, thereby reducing the deformation of the cap plate <NUM> and promoting the appearance and performance of the secondary battery. At the same time, by providing the second gap, it also can increase the distance between the insulating member <NUM> and the vent piece <NUM>, thereby avoiding the vent piece <NUM> being crushed.

The insulating member <NUM> has a third inner surface <NUM> at a side close to the electrode assembly <NUM>, and the third inner surface <NUM> is a flat surface. In the secondary battery, when the electrode units <NUM> expand, the expansions of the electrode units <NUM> will be accumulated in the axial direction Z, thereby leading to the electrode unit <NUM> contacting the third inner surface <NUM> of the insulating member <NUM>, and even pressing the third inner surface <NUM>. If the third inner surface <NUM> is uneven, a force applied to the electrode unit <NUM> by the third inner surface <NUM> is uneven too, thereby leading to local deformation of the electrode unit <NUM> being serious, resulting in the electrode plate of the electrode unit <NUM> fracturing, and causing safety risk. In the present invention, the third inner surface <NUM> is a flat surface, so when the electrode units <NUM> expand, it can avoid the electrode unit <NUM> deforming uneven, prevent the electrode plate from fracturing and improve safety performance. In order to ensure that the electrode units <NUM> deform evenly, a flatness of the third inner surface <NUM> is smaller than or equal to <NUM>.

Referring to <FIG>, the electrode unit <NUM> is a flat structure formed by winding, a periphery of the electrode unit <NUM> forms a wide surface S1 and a narrow surface S2. The wide surface S1 is provided as two in number and the two wide surfaces S1 are respectively positioned at two ends of the electrode unit <NUM> in the axial direction Z, the narrow surface S2 is provided as two in number and the two narrow surfaces S2 are respectively positioned at two ends of the electrode unit <NUM> in the width direction Y. Each narrow surface S2 is in the shape of arc and connects the two wide surfaces S1.

The wide surface S1 is disposed to face the first inner surface <NUM>, the second inner surface <NUM> and the third inner surface <NUM> in the axial direction Z. Before the electrode units <NUM> expand, the wide surface S1 is approximately parallel to the first inner surface <NUM>, the second inner surface <NUM> and the third inner surface <NUM>. The wide surface S1 has a larger area, when the electrode units <NUM> expand, the wide surface S1 and the third inner surface <NUM> facing each other are easier to contact evenly; at the same time, the expanding force also is evenly transferred to the first inner surface <NUM>.

In the secondary battery, the electrode units <NUM> are directly stacked in the axial direction Z. Two adjacent electrode units <NUM> contact each other via the wide surfaces S1 thereof.

The cap assembly <NUM> in accordance with some embodiments further includes a protecting piece <NUM>, and the protecting piece <NUM> is welded with the cap plate <NUM> from outside and covers the through-hole <NUM>. The protecting piece <NUM> avoids foreign materials damaging the vent piece <NUM>.

Hereinafter a second embodiment of the secondary battery of the present invention will be described. In order to make description concise, hereinafter the differences between the second embodiment and the first embodiment are mainly described, the part which is not described can be understood with reference to the first embodiment.

Referring to <FIG>, compared to the first embodiment, the second groove <NUM> in the second embodiment is omitted. In the second embodiment, it simplifies the forming process of the cap plate <NUM> by omitting the second groove <NUM>. However, in the second embodiment, because the second groove <NUM> is omitted, when welding, the laser is easily blocked by the side wall of the first groove <NUM>, which leads to a higher requirement on incident angle and incident accuracy of the laser, and is not beneficial to industrial production. When the incident angle of the laser deviates, the laser is easy to act on the first inner surface <NUM>, and a welding region will be formed on the first inner surface <NUM>, the welding region is easy to pierce the insulating member <NUM>, thereby resulting in safety risk.

Referring to <FIG>, compared to the first embodiment, a third embodiment omits the first groove <NUM> and the second groove <NUM>.

Specifically, the cap plate <NUM> is provided with a third groove <NUM>, the third groove <NUM> is provided at a side of the cap plate <NUM> away from the electrode assembly <NUM>, and the third groove <NUM> is disposed along a periphery of the through-hole <NUM>. The third groove <NUM> in the shape of annulus. The vent piece <NUM> is provided in the third groove <NUM>.

In the third embodiment, the vent piece <NUM> is provided at an outer side of the cap plate <NUM>, so a distance between the vent piece <NUM> and the insulating member <NUM> is larger; when the electrode units <NUM> expand, the vent piece <NUM> is not easily crushed.

Claim 1:
A secondary battery, comprising an electrode assembly (<NUM>), a case (<NUM>) and a cap assembly (<NUM>);
the case (<NUM>) having an accommodating cavity (<NUM>), the accommodating cavity (<NUM>) having an opening at an end of the case (<NUM>) in an axial direction (Z), and the electrode assembly (<NUM>) being accommodated in the accommodating cavity (<NUM>);
the electrode assembly (<NUM>) comprising electrode units (<NUM>), and the electrode units (<NUM>) being stacked in an axial direction (Z) of the accommodating cavity (<NUM>); the electrode unit (<NUM>) being a flat structure and having two wide surfaces (S1) and two narrow surfaces (S2), the two wide surfaces (S1) being respectively positioned at two ends of the electrode unit (<NUM>) in the axial direction (Z), the two narrow surfaces (S2) being respectively positioned at two ends of the electrode unit (<NUM>) in the width direction (Y); the narrow surface (S2) being connected with the wide surface (S1);
the cap assembly (<NUM>) comprising a cap plate (<NUM>) and a vent piece (<NUM>), the cap plate (<NUM>) being connected with the case (<NUM>) and positioned at a side of the electrode assembly (<NUM>) in the axial direction (Z);;
the cap plate (<NUM>) being provided with a through-hole (<NUM>), the vent piece (<NUM>) being connected with the cap plate (<NUM>) and covering the through-hole (<NUM>);
the cap plate (<NUM>) having a first inner surface (<NUM>) at a side close to the electrode assembly (<NUM>), the vent piece (<NUM>) having a second inner surface (<NUM>) at a side close to the electrode assembly (<NUM>), and a distance (d2) between the first inner surface (<NUM>) and the electrode assembly (<NUM>) being smaller than a distance d1) between the second inner surface (<NUM>) and the electrode assembly (<NUM>).