Description:Field of the Invention
The subject matter of the present disclosure broadly relates to the field of battery. Particularly, the present disclosure relates to surface modification of the tab on the electrode foil for a secondary battery.
Background of the Invention
Rechargeable or secondary batteries, particularly lithium-ion (Li-ion) batteries, have garnered significant attention in recent years due to their widespread applications across various domains, including electric vehicles, smartphones, laptops, power tools, and more. These batteries are favored for their numerous advantages, such as being eco-friendly, cost-effective due to their rechargeability, and providing high power output. As a result, considerable research is focused on enhancing their performance and efficiency.
Among the various types of secondary batteries, Li-ion batteries are of particular interest because of their light weight, high energy density, and low maintenance requirements. Li-ion batteries are available in different formats, including cylindrical, prismatic, and pouch configurations. In all of these formats, a metal foil is coated with electroactive material and placed between separators, after which the assembly is formed into the desired shape. In the past, tabs were attached to the electrode foils to draw current. More recently, the uncoated portion of the electrode metal foil itself is utilized as the tab, simplifying the manufacturing process compared to the traditional method of connecting external tabs.
These tabs are typically folded in a uniform or non-uniform manner and welded to the current collector disc, which is then connected to the electrode terminal. However, the force applied during the folding/bending process can sometimes cause damage to the tabs, or result in the formation of metal particles that enter the jelly-roll assembly. These particles can damage the separator, potentially leading to short-circuiting. Also when the tab portion is subjected to non-uniform bending such as crushing, the force applied will damage the coated electrode resulting the cell failure. To mitigate this risk, the bending area is often weakened to prevent rebound and reduce the likelihood of fracture.
While this approach is beneficial for uniformly folded tabs, it is less effective for non-uniformly bent tabs. In such cases, the bending may cause stress concentrations, increasing the likelihood of damage or failure in the scored region. Therefore, there is a need for an improved solution to prevent damage and eliminate the rebound effect during irregular tab bending, ensuring the integrity of the tabs and the overall performance of the battery.
Brief Description of Figures
Fig. 1a depicts the perspective view of the jelly-roll without the surface modification of the tabs for a cylindrical battery cell, according to embodiments as disclosed herein;
Fig. 1b depicts the perspective view of the jelly-roll with the surface modification of the tabs for a cylindrical battery cell, according to embodiments as disclosed herein;
Fig. 2 depicts a sectional view of the electrode foil with the surface modification of the tabs, according to embodiments as disclosed herein;
Fig. 3 depicts the exploded view of the jelly roll, according to embodiments as disclosed herein;
Detailed description of the invention
The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
As discussed in the background, there is a dire need for the improvement of tab scoring for a non-uniformly bent electrode. The present subject matter relates to the tab scoring design for a rolled electrode assembly. More particularly the present invention is directed towards a tab scoring design for a non-uniformly bent rolled electrode assembly.
Figure 1a is the perspective view of the jelly roll (100) before tab modification and Figure 1b is the perspective view of the jelly roll after tab modification. The negative electrode (150) and the positive electrode (130) are wound using a mandrel to form a jelly roll (100) with a separator (140) stacked in between, at the top and at the bottom. The separator serves as an ionic conductor at the same time blocking the flow of electrons, thus preventing short-circuit. The negative electrode is longer and wider than the positive electrode in order to avoid the Li plating during the charging and discharging process. The positive electrode active material is coated over an aluminum foil to form a positive electrode or cathode whereas the negative electrode active material is coated over a copper foil to form the negative electrode or anode.
Alternative to boehmite coating as boehmite coated electrodes will end up formation of more air gaps and one line of etching is given as this results in more weakened parts during welding and damages the tab region.
The electrode comprises an active material-coated portion (100B) and an uncoated portion (100A). The uncoated portion of the electrode foil, located above the active material-coated portion, functions as tabs for the secondary battery. Figure 1b provides a perspective view of a jelly roll (100) featuring surface-modified tabs. The active material-coated portion is coated with one or more active materials selected from a group consisting of transition metal oxides, olivine phosphates, spinel oxides, natural graphite, artificial graphite, LTO, silicon or silicon/ Carbon composites.
Fig. 2 provides the sectional view of the current collector foil (160). The uncoated portion of the electrode is further divided into three distinct regions: A, B, and C. Region A functions as a buffer region, located between the active material-coated portion and the tab surface modification region. The height of Region A is between 1 mm and 1.5 mm. This buffer region acts as a cushioning layer, designed to mitigate the effects of bending forces applied to the tabs, ensuring proper tab bending while minimizing or eliminating air gaps. The reduction or absence of air gaps in the tab region enhances the weldability of the tabs and ensures a strong, reliable connection between the tabs and the current collector after welding. Furthermore, during the welding process, Region A serves to confine the heat-affected zone to within this region, preventing excessive heat from reaching the active material-coated portion and thereby safeguarding the integrity of the active material from thermal damage.
As illustrated in Figure 2, Region B represents the surface-modified tab portion, situated above the buffer region (Region A) and below the tab region (Region C). The surface modification is achieved by etching the uncoated electrode foil to a depth of 2 µm using a laser beam. The width of the etched region ranges from 5 mm to 15 mm, with a more specific range of 9 mm to 12 mm. These dimensions are carefully selected to ensure optimal performance: widths below this range may not provide adequate space for bidirectional bending of the tabs, while widths above this range may result in unidirectional bending rather than bidirectional bending. The height of the etched portion is maintained at 1 mm. This height is kept constant to ensure sufficient space for tab formation while preserving the mechanical strength of the tabs. The surface modification in Region B enhances the flexibility and durability of the tabs, enabling them to withstand bending forces without compromising structural integrity.
As depicted in Figure 2, the invention employs a bidirectional etching process, wherein etching is performed on two sides of the current collector foil (100). Specifically, etching 110 is applied to the front side, and etching 120 is applied to the back side of the electrode foil. The tab surface modification is achieved through discontinuous etching, with etching performed on alternate sides of the foil. In Figure 2, the region G represents the gap between the two alternate etched regions 110 and 120 on the front and the back sides of the electrode foils, respectively. This gap has a width ranging from 1 mm to 3 mm and a height of 1 mm.
The inclusion of this gap is critical to the etching process. During laser etching, there is a possibility of the etching extending slightly beyond the predetermined range. Without the gap between the alternate etched portions, the laser may inadvertently penetrate into the adjacent etched region, resulting in excessive etching depth. Such over-etching can lead to the loss of excessive material from the foil, weakening the tabs and making them susceptible to damage during the bidirectional bending process. The gap region (zzz) thus serves as a buffer zone during the etching process, ensuring that the laser does not overlap into adjacent etched areas.
The tabs are folded non-uniformly by holding the battery in a holder and applying force through a jig. During this operation, as the foil regions are of the same thickness everywhere, the bending will leave air gaps in between that results in improper welding and also penetration of foreign particles inside the jelly roll. In the present invention, the scoring or etching is performed at alternative sides to allow the uniform and more distribution of stress particularly in the etched region thus allowing the bending to be thick and with minimal air gap formation. The region below the etched surface thus serves as a sacrificial region during the non-uniform bending operation thus protecting the anode and the cathode layers.
, Claims:We claim:
1. A jelly-roll (100) type electrode assembly comprising:
a negative electrode (150) and a positive electrode (130) stacked and wound together with a separator (140) interposed between them;
wherein each of the negative and positive electrodes includes a coated portion containing the electrode active material and an uncoated portion forming a tab region connected to the current collector; and
the tab region being divided into three distinct regions that facilitate non-uniform bending of the tab during formation.
2. The jelly-roll of claim 1, wherein the three distinct regions comprises region A, region B and Region C.
3. The jelly-roll of claim 2, wherein the region A is a buffer region located between the active material-coated portion (100B) and the tab surface modification region.
4. The jelly-roll of claim 2, wherein the region B is a surface-modified tab portion situated above Region A.
5. The jelly-roll of claim 2, wherein the region C the tab region that is located above region B which is connected to the current collector plate (100).
6. The jelly-roll of claim 4, wherein the surface modification of region B is done by chemical or laser etching.
7. The jelly-roll of claim 4, wherein the surface modification is done on alternative sides of the foil.
8. The jelly-roll of claim 5, wherein the region C is subjected to bidirectional bending.
9. The jelly-roll of claim 1, wherein the negative electrode (150) is coated with an active material over a copper foil, and the positive electrode (130) is coated with an active material over an aluminum foil.
10. A secondary battery comprising:
a jelly-roll (100) as claimed in claim 1 and
a cylindrical can accommodating the jelly-roll (100).