Electrode assembly and secondary battery

The present disclosure provides an electrode assembly and a secondary battery. The electrode assembly includes a first electrode plate, a second electrode plate and a separator. The first electrode plate, the second electrode plate and the separator are wound to a flat structure, and the flat structure comprises a main region and corner regions, the corner regions are provided at two ends of the main region along a width direction of the main region. The first electrode plate and the second electrode plate each are wound to turns. A gap is provided between two adjacent turns of the first electrode plate, the gap includes a first gap and a second gap. The first gap corresponds to the corner region in position, the second gap corresponds to the main region in position, and a dimension of the first gap is larger than a dimension of the second gap.

TECHNICAL FIELD

The present disclosure relates to the field of battery, and specifically relates to an electrode assembly and a secondary battery.

BACKGROUND

Existing secondary battery generally uses a wound electrode assembly, and the electrode assembly is formed by winding a positive electrode plate, a negative electrode plate and a separator. In a charge-discharge process of the secondary battery, volume expansions of the electrode plates occur due to a lithium deintercalation state and a lithium intercalation state of an active material, and an expanding stress will be generated between the positive plate and the negative electrode plate due to the expansions, and if the expanding stress is not effectively released, the wound electrode assembly will be distorted. Particularly, in a corner region of the electrode assembly which is formed by winding, the expanding stress is most concentrated, and the distortion of the electrode assembly is more prone to occur. Further, at the later stage of the cycle, the expanding stress will extrude an electrolyte between the positive plate and the negative electrode plate, which results in infiltration capability of the electrode assembly being poor.

SUMMARY

An electrode assembly in accordance with some embodiments comprises a first electrode plate, a second electrode plate and a separator, the separator separates the first electrode plate and the second electrode plate. The first electrode plate, the second electrode plate and the separator are wound to a flat structure, and the flat structure comprises a main region and corner regions, the corner regions are provided at two ends of the main region along a width direction of the main region. The first electrode plate and the second electrode plate each are wound to turns. A gap is provided between two adjacent turns of the first electrode plate, the gap comprises a first gap and a second gap. The first gap corresponds to the corner region in position, the second gap corresponds to the main region in position, and a dimension of the first gap is larger than a dimension of the second gap.

DETAILED DESCRIPTION

To make the object, technical solutions and advantages of the present disclosure more apparent, hereinafter the present disclosure 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 disclosure but are not intended to limit the present disclosure.

In the description of the present disclosure, unless otherwise specifically defined and limited, the terms “first”, “second”, “third”, etc. 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 disclosure can be understood according to the specific situation.

In the description of the present disclosure, 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 disclosure. Hereinafter the present disclosure will be further described in detail in combination with the exemplary embodiments and the figures.

Referring toFIG.1, a secondary battery in some embodiments of the present disclosure is a prismatic lithium-ion battery. Specifically, the secondary battery includes an electrode assembly1, a case2and a cap assembly3.

The case2forms an accommodating cavity21inside, so as to accommodate the electrode assembly1and an electrolyte. An opening is formed at an end of the case2along an axial direction Z, and the electrode assembly1can be placed into the case2via the opening. In some embodiments, the case2is made of a conductive metal such as aluminum or aluminum alloy. The axial direction Z is parallel to a height direction of the secondary battery, and the axial direction Z is perpendicular to a transverse direction X and a longitudinal direction Y of the secondary battery.

The case2in accordance with some embodiments includes first side plates22and second side plates23, the first side plates22are respectively positioned at two sides of the electrode assembly1along the longitudinal direction Y, the second side plates23are respectively positioned at two sides of the electrode assembly1along the transverse direction X, the first side plates22and the second side plates23are connected together to form the accommodating cavity21which is rectangular. An area of the first side plate22is larger than an area of the second side plate23.

The electrode assembly1in accordance with some embodiments is provided as plurality in number, and the plurality of electrode assemblies1are stacked sequentially along the longitudinal direction Y. Referring toFIG.2, each electrode assembly1includes a first electrode plate11, a second electrode plate12and a separator13, and the separator13separates the first electrode plate11and the second electrode plate12.

The cap assembly3includes a cap plate31, an electrode terminal32, an insulating member33and a current collecting member34. The cap plate31is connected with the case2and covers the opening of the case2, so as to seal the electrode assembly1in the accommodating cavity21of the case2. The insulating member33is provided at an inner side of the cap plate31, so as to separate the cap plate31and the electrode assembly1. The electrode terminal32is provided to the cap plate31and protrudes to an outside of the cap plate31. The electrode terminal32and the current collecting member34each are provided as two in number, one current collecting member34connects the first electrode plate11and one electrode terminal32, the other current collecting member34connects the second electrode plate12and the other electrode terminal32.

Referring toFIG.2, the first electrode plate11, the second electrode plate12and the separator13are wound to a flat structure, and the first electrode plate11, the second electrode plate12and the separator13each are wound to turns. In the forming process, the first electrode plate11, the second electrode plate12and the separator13are fixed to a winding mandrel, and then the first electrode plate11, the second electrode plate12and the separator13are spirally wound to form a winding body by rotating the winding mandrel. The winding mandrel is taken out from the winding body after winding; finally, the winding body is pressed to a flat shape.

The flat structure includes a main region14and corner regions15, the corner regions15are provided at two ends of the main region14in a width direction of the main region14. In some embodiments of the present disclosure, the width direction of the main region14is parallel to the axial direction Z.

In the main region14, the first electrode plate11and the second electrode plate12each are divided into a plurality of layers along a thickness direction of the main region14, the thickness direction of the main region14is parallel to the longitudinal direction Y of the secondary battery. Before expanding, each layer of the first electrode plate11in the main region14is substantially perpendicular to the longitudinal direction Y, each layer of the second electrode plate12in the main region14is substantially perpendicular to the longitudinal direction Y.

In the corner region15, the first electrode plate11and the second electrode plate12each are divided into a plurality of layers along a direction away from a winding center; each layer of the first electrode plate11in the corner region15is substantially in the shape of circular arc, each layer of the second electrode plate12in the corner region15is substantially in the shape of circular arc.

In the charge-discharge process, volume expansions of the first electrode plate11and the second electrode plate12occur, and an expanding stress will be generated between the first electrode plate11and the second electrode plate12due to the expansions, if the expanding stress is not effectively released, the electrode assembly1will be easy to deform. Meanwhile, the expanding stress will extrude the electrolyte between the first electrode plate11and the second electrode plate12, which results in infiltration capability of the electrode assembly1being poor.

In some embodiments, a gap is provided between two adjacent turns of the first electrode plate11in the present disclosure, the gap includes a first gap G1and a second gap G2. The first gap G1corresponds to the corner regions15in position, and the second gap G2corresponds to the main region14in position. A dimension of the first gap G1is larger than a dimension of the second gap G2.

In the present disclosure, by providing the first gap G1and the second gap G2, an expansion space can be reserved for the first electrode plate11and the second electrode plate12, thereby releasing the expanding stress, reducing deformation degree of the electrode assembly1. Meanwhile, the electrolyte can also enter into the inside of the electrode assembly1via the first gap G1and the second gap G2, thereby improving the infiltration capability, and reducing a risk of lithium precipitation.

In the corner region15, a distance between two adjacent layers of the first electrode plate11is defined as d1, and two layers of the separator13and one layer of the second electrode plate12are provided between the two adjacent layers of the first electrode plate11, therefore, a value obtained by that the d1minus a thickness of the two layers of the separator13and a thickness of the one layer of the second electrode plate12is the dimension of the first gap G1.

Similarly, in the main region14, a distance between two adjacent layers of the first electrode plate11is defined as d2, and two layers of the separator13and one layer of the second electrode plate12are provided between the two adjacent layers of the first electrode plate11, and a value obtained by that the d2minus a thickness of the two layers of the separator13and a thickness of the one layer of the second electrode plate12is the dimension of the second gap G2.

When the electrode assembly1expands, the stress in the corner regions15is most concentrated, and the corner regions15is most prone to deform. Taking one turn of the first electrode plate11as an example, referring toFIG.6, when expanding, the main region14expands most seriously in a central region (at a line L1) along the axial direction Z; meanwhile, the first electrode plate11is stretched when expanding, so a certain tension is generated inside. At L1where the expansion is most serious, the first electrode plate11is subjected to a combination of two tensions F1and F4, F1and F4limit the expansion of the first electrode plate11in the main region14; taking F1as an example, F1is decomposed into two component forces F11and F12, F4is decomposed into two component forces F41and F42, F11and F41cancel each other, therefore, F12and F42will affect the deformation of the first electrode plate11in the main region14.

Similarly, when expanding, two ends of the first electrode plate11in the corner region15are also subjected to two tensions, that is F2and F3. A component force F21of F2and a component force F31of F3will pull the first electrode plate11in the corner region15along the axial direction Z, a component force F22of F2and a component force F32of F3will pull the first electrode plate11in the corner region15along the longitudinal direction Y; and since the first electrode plate11in the corner region15is in the shape of arc, F22and F32cannot cancel each other; under the action of the combination of F2and F3, the first gap G1will be seriously reduced. Therefore, in the electrode assembly1, the stress in the corner region15is more concentrated; meanwhile, since the first electrode plate11and second electrode plate12in the corner region15are in the shape of arc, the first electrode plate11and second electrode plate12in the corner region15are easier to deform under the action of the stress. When the stress is excessively large, the first electrode plate11and the second electrode plate12in the corner region15are easy to fracture.

Since the stress in the corner region15is more concentrated, therefore, if the dimension of the first gap G1is equal to the dimension of the second gap G2, when the electrode assembly1expands and deforms, a reduced extent of the first gap G1will be greater than a reduced extent of the second gap G2. That is, if an initial dimension of the first gap G1is equal to an initial dimension of the second gap G2, when the secondary battery is cycled to a certain extent, the dimension of the first gap G1will be smaller than the dimension of the second gap G2. At this time, the electrolyte in the main region14is more than the electrolyte in the corner region15, which results in a difference between the infiltration capability of the main region14and the infiltration capability of the corner region15, and affects the consistency of the dynamic performance of the electrode assembly1.

Therefore, in some embodiments of the present disclosure, the dimension of the first gap G1is larger than the dimension of the second gap G2, such that a volume of the electrolyte in the first gap G1is larger than a volume of the electrolyte in the second gap G2before expanding. In the present disclosure, by increasing the first gap G1, the stress in the corner region15is released in time, which avoids the first electrode plate11and the second electrode plate12in the corner region15being fractured. Compared to the first gap G1, the second gap G2has a smaller dimension, and has a smaller influence on a thickness of the secondary battery along the longitudinal direction Y. Since the stress in the corner region15is greater, therefore, when the secondary battery is cycled to a certain extent, the dimension of the first gap G1will be substantially equal to the dimension of the second gap G2, so that the volume of the electrolyte in the first gap G1is substantially equal to the volume of the electrolyte in the second gap after expanding, thereby decreasing the difference between the infiltration capability of the main region14and the infiltration capability of the corner region15to a certain extent, and ensuring the consistency of the dynamic performance of the electrode assembly1.

In addition, when the main region14expands to a certain extent, the main region14will be attached to the first side plates22of the case2, so the first side plates22can limit the deformation of the main region14even if the second gap G2is smaller. While the corner regions15are in the shape of arc, the case2and the cap plate31cannot limit the distortion of the corner regions15, so the first gap G1needs to have a larger dimension.

A ratio of the dimension of the first gap G1to the dimension of the second gap G2is less than 16. If the ratio of the dimension of the first gap G1to the dimension of the second gap G2is too large, there will be a larger difference between a diameter of the corner region15and the thickness of the main region14, which results in significant traces at junctions of the main region14and the corner regions15, and affects the flatness of the electrode assembly1.

The dimension of the first gap G1is 20 μm-80 μm. If the dimension of the first gap G1is less than 20 μm, the stress cannot be sufficiently released, which results in the distortion of the corner region15. If the dimension of the first gap G1is larger than 80 μm, the lithium-ion transmission path will be too long, and lithium precipitation is easy to occur.

The dimension of the second gap G2is 5 μm-20 μm. The main region14will press the first side plate22when the main region14expands, under the action of the expanding stress of the main region14and a reaction force of the first side plate22, the second gap G2easily disappears, which leads to the electrolyte being extruded out of the main region14, and causes cycle diving. If the dimension of the second gap G2is larger than 20 μm, the thickness of the main region14will be increased to a larger extent, and the energy density of the secondary battery is lowered.

The second electrode plate12is provided with a first protrusion P1and a second protrusion P2, the first protrusion P1corresponds to the corner region15in position, the second protrusion P2corresponds to the main region14in position. The first protrusion P1and the second protrusion P2protrude toward the same side of the second electrode plate12. A height h1of the first protrusion P1is larger than a height h2of the second protrusion P2.

The first protrusion P1and the second protrusion P2can be formed by stamping the second electrode plate12. Referring toFIG.4, after forming, a recess is formed at an inner side of the first protrusion P1and a recess is formed at an inner side of the second protrusion P2.

In the present disclosure, by providing the first protrusion P1on the second electrode plate12, the distance d1between the two adjacent layers of the first electrode plate11in the corner region15can be increased, thereby forming the first gap G1between the two adjacent layers of the first electrode plate11. By adjusting the value of h1, the dimension of the first gap G1can be adjusted.

Similarly, in the present disclosure, by providing the second protrusion P2on the second electrode plate12, the distance d2between the two adjacent layers of the first electrode plate11in the main region14can be increased, thereby forming the second gap G2between the two adjacent layers of the first electrode plate11. By adjusting the value of h2, the dimension of the second gap G2can be adjusted.

The first protrusion P1can be circular, elongated, polygonal or elliptical. Referring toFIG.4, the first protrusion P1is circular and provided as plurality in number, and the plurality of first protrusions P1are arranged in array; the second protrusion P2is circular and provided as plurality in number, and the plurality of second protrusions P2are arranged in array. Alternatively, referring toFIG.6, the first protrusion P1also can be elongated and provided as plurality in number, the second protrusion P2also can be elongated and provided as plurality in number.

The separator13includes a first separator131and a second separator132, the first separator131and the second separator132are respectively positioned at two sides of the second electrode plate12. The first separator131and the second separator132each are wound to turns, one turn of the first separator131and one turn of the second separator132are provided between two adjacent turns of the first electrode plate11.

The first protrusion P1and the second protrusion P2protrude toward the first separator131. Referring toFIG.2, in the corner region15, a third gap G3is kept between the second electrode plate12and the first separator131, and a dimension of the third gap G3is equal to the height of the first protrusion P1; in other words, the first separator131is attached to a top end of the first protrusion P1. In the main region14, a fourth gap G4is kept between the second electrode plate12and the first separator131, and a dimension of the fourth gap G4is equal to the height of the second protrusion P2; in other words, the first separator131is attached to a top end of the second protrusion P2. The dimension of the third gap G3is larger than the dimension of the fourth gap G4.

Referring toFIG.2andFIG.3, the second electrode plate12includes a first region121and a second region122. The first region121corresponds to the corner region15in position, in other words, the first region121is the layer of the second electrode plate12in the corner region15. The second region122extends from an end of the first region121and corresponds to the main region14in position, that is, the second region122is the layer of the second electrode plate12in the main region14.

The first region121is provided with the first protrusions P1, and a ratio of an area of the first protrusions P1to an area of the first region121is 50%-90%. If the area ratio is more than 90%, a density of the first protrusions P1will be too large, and the second electrode plate12is easily crushed in the forming process. If the area ratio is less than 50%, the first protrusions P1will be weak in overall strength, and easily flattened in the winding process.

Similarly, the second region122is provided with the second protrusions P2, and a ratio of an area of the second protrusions P2to an area of the second region122is 50%-90%. If the area ratio is more than 90%, a density of the second protrusions P2will be too large, and the second electrode plate12is easily crushed in the forming process. If the area ratio is less than 50%, the second protrusion P2will be weak in overall strength, and easily flattened in the winding process.

The first electrode plate11is a negative electrode plate, the first electrode plate11includes a copper foil and a negative active material coated on a surface of the copper foil, the negative active material includes a graphite or silicon. Correspondingly, the second electrode plate12is a positive electrode plate, the second electrode plate12includes 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 material of the second electrode plate12is softer and has a good elasticity, so the second electrode plate12is easily pressed to form the first protrusion P1and the second protrusion P2and not easy to fracture.

A ratio of a width w of the main region14along the axial direction Z to a thickness t of the main region14along the longitudinal direction Y is 5-20. Referring toFIG.6, the larger the width of the main region14is, the smaller an extended rate is when expanding, the smaller the tension in the first electrode plate11is, the lower the stress concentration of the corner region15is, and the smaller the deformation of the corner region15is. Certainly, if w/t is too large, such as larger than 20, the electrode assembly1will be too flat to satisfy requirement of the shape of the secondary battery.

In the main region14, the number of layers of the first electrode plate11is even, the number of layers of the second electrode plate12is even. That is, the layers of the first electrode plate11respectively positioned at two sides of the winding center along the longitudinal direction Y are identical in number, the layers of the second electrode plate12respectively positioned at two sides of the winding center along the longitudinal direction Y are identical in number. In the present disclosure, the number of layers of the first electrode plate11in the main region14is configured as even, and the number of layers of the second electrode plate12in the main region14is configured as even, the symmetry of the main region14with respect to the winding center is promoted, the expanding stresses at two sides of the winding center in the longitudinal direction Y are equal, the uniformity of the expansion of the main region14is improved, the local deformation of the electrode assembly1is reduced, and the electrode plate is avoided being fractured.