WO2024028887A1

WO2024028887A1 - A cylindrical secondary battery

Info

Publication number: WO2024028887A1
Application number: PCT/IN2023/050512
Authority: WO
Inventors: Guruprasad S. HEGDE; M. Vanitha; Rajesh K
Original assignee: Ola Electric Mobility Limited
Priority date: 2022-08-01
Filing date: 2023-06-01
Publication date: 2024-02-08

Abstract

Described herewith is a tabless alkali ion secondary cylindrical cell design. The cylindrical cell includes a sandwich of a cathode, a separator and an anode winded in the form of a jelly roll and accommodated in a cylindrical case. The disclosure describes a method to prepare the positive and negative electrodes with a group of flag-like structures. The positive and negative flag groups are separately arranged at one side of a jelly roll to facilitate the electrolyte infiltration.

Description

A CYLINDRICAL SECONDARY BATTERY

FIELD

[0001] Various embodiments of the present disclosure relate generally to secondary cells. More specifically but not exclusively to a cylindrical secondary cell and a method of assembling the cylindrical secondary cell.

BACKGROUND

[0002] Generally, a secondary cell, also known as a battery cell, can be electrically recharged after use to its original pre-discharge condition. Recharge of the battery cell may be achieved by passing a current through it in a direction opposite to the direction of current discharge. Several types of battery cells are at present used in energy storage applications. In most applications, the battery cells are in cylindrical and hence, the battery cells are interchangeably referred to as cylindrical cells. The cylindrical cell used in alkali ion batteries employ a jelly roll pattern, where the positive electrode, the separator and negative electrodes are rolled together, and the positive and negative current collectors are separately welded to electrically conducting strips called “tabs.” The positive and negative tabs are connected to a cell can and cap of the cylindrical cell, respectively. Electric current travels by means of these tabs to connectors located on the outside of the battery cell. In some of such traditional designs, the current travels all the way along the jelly roll and passes to the outer circuit through the cell tabs. The ohmic resistance of the cell tabs may cause power loss thereby contributing to the rise of the cell temperature and acting as a limiting factor to the current carrying capacity of the cell.

[0003] Further, the electric current from all over the length of the cell must pass through the cell tabs. In some of the traditional cylindrical cell designs, the tab dimensions are considerably smaller when compared to the overall current collector and hence act as a bottleneck for the electrical current flow. To overcome the problems associated with the conventional tab design, the tabs are replaced with flag-like protrusions from the positive and negative current collectors, which are folded perpendicular to the axis of the jelly roll to form an interleaved pattern. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1(a) is a schematic diagram of an electrode current collector according to an embodiment of the present disclosure;

[0005] FIG. 1 (b) is a schematic diagram illustrating a flag portion of the electrode current collector according to an embodiment of the present disclosure;

[0006] FIG. 2(a) is a schematic diagram that illustrates a negative electrode, a separator, and a positive electrode according to an embodiment of the present disclosure.

[0007] FIG. 2(b) is a schematic diagram that illustrates a jelly roll of a battery cell according to an embodiment of the present disclosure.

[0008] FIG. 3(a) illustrates a bottom view of the jelly roll according to an embodiment of the present disclosure.

[0009] FIG. 3(b) illustrates a top view of the jelly roll which remains empty without any flags according to an embodiment of the present disclosure.

[0010] FIG. 4(a) illustrates a bottom view of the jelly roll with positive and negative flags connected to corresponding current collectors according to an embodiment of the present disclosure.

[0011] FIG. 4(b) illustrates a lateral view of the jelly roll of an energy storage cell according to an embodiment of the present disclosure.

[0012] FIG. 5 is a schematic diagram of a cylindrical cell according to an embodiment of the present disclosure.

[0013] FIG. 6 is a block diagram for a method of constructing an energy storage cell according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0014] An electrochemical cell primarily consists of a positive electrode and a negative electrode. An electrolyte sandwiched between the positive and negative electrodes provides a pathway for the ions to shuttle between the positive and negative electrodes. In an alkali ion cell, the negative or the positive electrode consists of corresponding anode/cathode materials coated on suitable metallic substrates called current collectors. A membrane usually made of a single or multiple polymer layers called a “separator” is sandwiched between the positive and negative electrodes. The separator holds the liquid electrolyte in its pores and provides ionic contact between the electrodes.

[0015] A cylindrical cell is a cell format in alkali metal ion cell systems, where a long positive electrode-separator-negative electrode sandwich is rolled in the form of a cylinder called a “jelly roll”. The jelly roll is enclosed in a cylindrical stainless steel can. An electrolyte is then filled inside and the can is sealed with a stainless-steel cap. The cap and can are insulated from each other, and act as two electrical contact terminals for the electrochemical cell. The positive and negative current collectors of the jelly roll are welded to suitable metallic strips called tabs. The positive and negative tabs are connected to the cell can and cap (or vice versa) respectively. The cell tabs provide electrical contact to the jelly roll from the external circuit. This design offers high energy density since higher loading of electrode materials can be achieved in a small cylindrical volume.

[0016] In some other battery cell designs, tabless cell designs are proposed to reduce the ohmic resistance by replacing the existing tabs with a number of flag-like protrusions from the positive and negative current collectors. The flags are folded perpendicular to the axis of the jelly roll to form an interleaved flower-like pattern. The interleaved flags of positive and negative electrodes lie at the top and bottom of the jelly roll, respectively, or vice-versa. The interleaved pattern serves as the electrical contact, from which the electric current passes through the cell. This design reduces the need for an additional tab, reduces the overall electrical resistance and improves the current carrying capacity of the cell. However, after the jelly roll is prepared, an electrolyte is added to facilitate the ion transfer between the anode and cathode. Non-uniform distribution of the electrolyte in the cell may result in certain cell regions becoming inactive, decreasing the overall performance of the cell. In addition, the inactive regions can become the sites for lithium plating which are detrimental to cell performance and safety. Some of the existing flag configurations of a battery cell may affect the uniform distribution of the electrolyte thereby causing one or more aforementioned shortcomings. The present disclosure relates to an electrochemical cell for energy storage devices. Particularly, the present disclosure relates to a cylindrical cell that is often used in alkali ion batteries. Accordingly, disclosed herewith is a cylindrical cell design that facilitates uniform electrolyte distribution in the cell.

[0017] Referring to FIGs 1(a) to 5, FIG. 1(a) is a schematic diagram of an electrode plate according to an embodiment of the present disclosure. The electrode plate 100 comprises an active electrode material 102 coated on a metallic current collector 104, leaving an uncoated portion on one side. In the illustrative embodiment of Fig 1 (a), a bottom portion of the metallic current collector 104 is coated with electrode material 102 and a top portion is uncoated, which forms the uncoated portion. The uncoated portion of the current collector 104 is modified in the form of a single or a group of flags 104a, which acts as current carrying tabs. The flag(s) 104a runs along a longitudinal axis (i.e., length direction as illustrated in FIG. 1 (a)) of the current collector 104. In an embodiment, the electrode plate 100 is an anode. Accordingly, as used herein, a coated portion and an uncoated portion of the anode are referred to as an anode coated portion and an anode uncoated portion, respectively. The anode comprises an anode active material coated on the anode current collector forming the anode coated portion. Example anode active materials include but are not limited to graphite, hard carbon, carbonaceous materials like carbon nanotubes (CNTs), reduced graphene oxide (rGO), lithium titanate (LTO), a tin/cobalt alloy, silicon and silicon/carbon composites, all alloying and conversion anodes. In certain embodiments, the anode may comprise an anode collector and a coating of a lithium-ion active material on the current collector. Standard anode collector materials include but are not limited to aluminum, copper, nickel, stainless steel, carbon, carbon paper and carbon cloth. In one embodiment, the anode may be a sheet of lithium metal serving both as active material and a current collector.

[0018] In another embodiment, the electrode plate 100 is a cathode. The electrode plate 100 may include a cathode coated portion and a cathode uncoated portion. The cathode comprises a cathode active material coated on a cathode current collector that forms the cathode coated portion. The cathode used in the present disclosure can be selected from the group comprising but not limited to lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), lithium fluorophosphate (LFP), lithium nickel manganese cobalt oxide (NMC 111, NMC 532, NMC 622, NMC 811 or other stoichiometries), lithium iron aluminum nickelate (NFA), lithium cobalt aluminum nickelate (NCA), or the like. Standard cathode collector materials include but are not limited to aluminum.

[0019] FIG. 1(b) is a schematic diagram illustrating the flag portion of the electrode current collector according to an embodiment of the present disclosure. In an embodiment, the flags 104a are produced by forming slits on the uncoated portion of the current collector 104. In other words, due to the formation slits, the flags 104a appear to be extending outward and separated from each other in the length direction. In an embodiment, the slits are formed by cutting or laser etching the current collector. The specification of the flag 104a such as width w, height h, angle of slanting a, distance between each flag d and a number of flags n in the flag group can be varied to befit the current density and cell design requirements.

[0020] The electrode plate 100 is rolled in a length direction along with other components of an energy storage cell to form a jelly roll structure. The width w and the distance d are measured in the length direction of the electrode plate 100. Hereinafter, the distance d is referred to as “flag distance” to differentiate it from other features discussed herein. The angle of slanting a is measured with reference to an axis of the energy storage cell. In one embodiment, the angle of slanting a is in the range of 60 to -60 degrees with reference to the longitudinal axis. Further, s illustrated in FIG. 1 (a), the electrode plate 100 comprises three flag groups and each flag comprises a number of flags n. Each flag group comprises a number of flags n. In one embodiment, the number of flags n for each flag group can be uniform. In another embodiment, the number of flags n for one flag group may vary with the number of flags n in another flag group. Thus, making the number of flags n to be variable. In yet another embodiment, the number of flags n can be fixed for certain flag groups and variable for the remaining flag groups of an energy storage cell.

[0021] FIG. 2(a) is a schematic diagram that illustrates an anode, a separator, and a cathode according to an embodiment of the present disclosure. The anode 200a comprises the anode active material 202a coated on the anode current collector 204a. The uncoated portion of the anode current collector is provided with flags 206a. The flags 206a are made into groups such that the flag groups are separated by a distance x(t). This distance x(t) is referred to as “group distance” to differentiate it from the flag distance d. The group distance x(t) is a function of thickness t. According to some embodiment, each electrode may include two or more flag groups. FIG. 2 (a) illustrates two flag groups 206a that are separated from each other by the group distance x (t). As illustrated in FIG. 2 (b), the thickness t is measured from a centre of the jelly roll structure to an outer circumference of the energy storage cell. That is, in one embodiment, the thickness t can be a radius of the energy storage cell. Accordingly, the group distance is configured based on the thickness to achieve the configuration(s) discussed herein for the energy storage cell in a jelly roll structure. In one embodiment, the group distance x(t) is fixed. In another embodiment, the group distance x(t) between the flag groups is varied. Further, within each flag group, the flags 206a of the anode 200a are adjusted such that when the anode is rolled, the flags 206a are aligned on a first side of the jelly roll. The first side is a first longitudinal side of the jelly roll and the opposite side can be a second longitudinal side of the jelly roll structure.

[0022] The cathode 200b comprises the cathode active material 202b coated on the cathode current collector 204b. The uncoated portion of the cathode current collector is provided with flags 206b. In a preferred embodiment, the flags 206b are provided in groups such that the flag groups are separated by a distance x’(t). The distance x’(t) represents a group distance of the cathode. According to some embodiment, the group distance of the cathode x’(t) can be different from the group distance x(t) of the anode. In one embodiment, the electrode that is placed outside with reference to the separator 200c can have a larger group distance when compared to an electrode that is placed inward of the separator 200c. In another embodiment, the distance between individual flags 206b is varied. The flags 206b of the cathode 200b are adjusted such that when the cathode 200b is rolled, the flags 206b are aligned on a second side of the roll that is opposite to the first side. In other words, in an axial view (i.e., viewed along a longitudinal axis of the energy storage cell), the energy storage cell can be substantially circular. The circular shape when partitioned into two imaginary halves, there can be two semi-circular portions or halves. In a preferred embodiment, the first side and the second side are in the first half and the second half of the jelly roll structure 200 respectively. Further, in one embodiment, the positive flag groups and the negative flag groups are folded in opposite directions during the winding. In a further embodiment, the flags can be folded inward, outward or selectively inward and outward.

[0023] The separator 200c may be a conventional separator membrane such as polypropylene (PP), polyethylene (PE), polypropylene (PP), polyethylene (PE) bilayer or PP/PE/PP tri-layer structure. The separator 200c is disposed in between the anode 200a and the cathode 200b to electrically insulate the anode from the cathode. [0024] FIGs. 3 (a) and 3 (b) show a bottom and top view of a jelly roll, respectively, according to an embodiment of the present disclosure. The jelly roll structure 200 is made by stacking the anode 200a, the separator 200c, the cathode 200b and the separator 200c and rolling, such that the anode flags 206a and the cathode flags 206b are disposed on one end of the jelly roll structure 200. In a preferred embodiment, the jelly roll structure 200 is formed such that the anode flags 206a and the cathode flags 206b are both on the bottom side of the jelly roll structure 200. In another embodiment, the anode flags 206a and the cathode flags 206b are provided on a top side of the jelly roll structure 200. Further, according to one embodiment, the anode flags 206a and the cathode flags are folded in opposite directions during the winding.

[0025] In a preferred embodiment, the anode flag groups 206a are aligned and folded at the left side and the cathode flag groups 206b are aligned folded at the right side of the jelly roll’s 200 bottom surface, as illustrated in FIG. 3 (a). In a further embodiment, the interleaved patterns form separate half-moon shaped anode and cathode current collector regions, at the bottom of the jelly roll. The advantage of such a design is that the top surface (as shown in FIG. 3 (b)) of the jelly roll is free of any flag-like structures which may otherwise inhibit electrolyte infiltration. Therefore, electrolyte infiltration can be performed effectively at the top of the jelly roll.

[0026] In another embodiment, the anode flag groups 206a are aligned and folded at the left side and the cathode flag groups 206b are aligned folded at the right side of the jelly roll’s 200 top surface. The interleaved patterns form separate half-moon shaped anode and cathode current collector regions, at the top of the jelly roll. The cathode and the anode current collector regions are having a substantial half-moon shape, as illustrated in FIG. 3 (a) a certain amount of gap is maintained between them for electrical isolation. The advantage of such a design with flags on one axial side (e.g., bottom side as per an illustrative embodiment of FIG. 3 (a)) is that the bottom surface of the jelly roll is free of any flag-like structures. Thus, the electrolyte infiltration can be performed effectively at the bottom of the jelly roll.

[0027] According to some embodiments, the interleaved current collector flags can be welded together and additionally to a suitable metallic current collector to improve the contact between each flag group. FIG. 4(a) illustrates a bottom view of the jelly roll with positive and negative flags connected to corresponding current collectors 207a, 207b according to an embodiment of the present disclosure. FIG. 4(b) illustrates a lateral view of the jelly roll after the flag group welding according to an embodiment of the present disclosure. As illustrated, according to some embodiments, the flags are compactly accommodated on the jelly roll structure 200 thereby making the energy storage cell compact. The jelly roll structure 200 is then assembled inside a cylindrical casing.

[0028] FIG. 5 is a schematic diagram of a cylindrical cell according to an embodiment of the present disclosure. The cylindrical cell 300 comprises a tubular body 302, a first cap 304 and a second cap 306. One of the first cap 304 or the second cap 306 includes two conductive terminals (Cl and C2) that are insulated from each other. Each terminal is made of a suitable metal(s) that can be welded or compressed against the respective flag groups to provide electrical contact. In an embodiment, the conductive terminal protrudes outside the cap. One of the conductive terminals is connected to the anode flag 206a and the other conductive terminal is connected to the cathode flag 206b, to define the anode terminal and the cathode terminal respectively. Once the jelly roll is placed inside the tubular body 302, the respective terminals are aligned and welded or compressed to the corresponding flag groups. Once the electrical contact is established, the cell cap can be closed so that the electrolyte infiltration can be carried out at the other open end of the cell-can. After the electrolyte infiltration, the cell-can’s open end can be closed with the second cap. In an embodiment, the gas venting safety mechanism shall be included near the second cap for improved cell safety. As discussed earlier, the flags can be provided on the top side or bottom side. In the illustrative embodiment of FIG. 5, the flags are provided on the top side such that they come in contact with the conductive terminals Cl and C2. In another embodiment, the flags can be provided on the bottom side and the second cap 306 with the conductive terminals Cl and C2 can enclose the tubular body 302 from the bottom side.

[0029] Now referring to FIG. 6, a flow diagram is illustrated for a method of constructing an energy storage cell according to an embodiment of the present disclosure. The method includes blocks 602-614. These blocks may not be performed in the same order and may include additional steps. Further, one or more steps may be performed more than one. Now referring to the method 600, the method of manufacturing/constructing the energy storage cells includes the following bocks. At block 602, an anode with an anode active material excluding an anode uncoated portion is provided. At block 604, a cathode with a cathode active material excluding a cathode uncoated portion is provided. At block 606, a separator configured to electrically isolate the anode and the cathode in a jelly roll structure of the energy storage cell is provided. At block 608, an anode flag group at the anode uncoated portion is provided. The anode flag group being disposed towards a first longitudinal side of the energy storage cell. At block 610, the anode flag group are aligned with each other. In one embodiment, the anode flag groups are aligned to be on a first side of a top/bottom side of the energy storage cell. At block 612, a cathode flag group at the cathode uncoated portion is provided. The cathode flag group being disposed towards the first longitudinal side of the energy storage cell. At block 614, the cathode flag group are aligned with each other and separating the cathode flag group from the anode flag group. The method may further include one or more steps are discussed in embodiments of the present disclosure.

[0030] While the present disclosure has been described with respect to certain number of embodiments, those skilled in the art, having benefit of the above description, will appreciate that other embodiments may be devised which do not depart from the scope of the present invention as described herein. In addition, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the claims.

Claims

CLAIMS What is claimed is:

1. An energy storage cell, comprising: an anode having an anode coated portion with an anode active material and an anode uncoated portion, and the anode uncoated portion comprises at least one anode flag group; a cathode having a cathode coated portion with a cathode active material and a cathode uncoated portion, and the cathode uncoated portion comprises at least one cathode flag group; and a separator disposed between the anode and the cathode to electrically isolate the anode and the cathode, wherein the anode, separator, and the cathode are rolled into a jelly roll structure of the energy storage cell, and wherein the at least one anode flag group and the at least one cathode flag group are disposed on a first longitudinal side of the jelly roll structure.

2. The energy storage cell of claim 1, wherein the at least one anode flag group are folded perpendicular to a longitudinal axis of the jelly roll structure in an interleaved pattern and the at least one anode flag group are accommodated within a first half moon portion at the first longitudinal side of the energy storage cell.

3. The energy storage cell of claim 1, wherein the at least one cathode flag group are folded perpendicular to a longitudinal axis of the jelly roll structure in an interleaved pattern and the at least one cathode flag group are accommodated within an second half moon portion at the first longitudinal side.

4. The energy storage cell of claim 1, wherein the anode, the separator, and the cathode are assembled in the jelly roll structure, such that flags corresponding to the anode flag group are connected to a first current collector and flags corresponding to the cathode flag group are connected to a second current collector.

5. The energy storage cell of claim 1, wherein the anode, the separator, and the cathode are disposed in a cylindrical casing.

6. The energy storage cell of claim 5, wherein the cylindrical casing comprises a tubular body, a first cap and a second cap, wherein the first cap is disposed at the first longitudinal side to enclose the tubular body thereat and the second cap is disposed at a second longitudinal side to enclose the tubular body thereat.

7. The energy storage cell of claim 6, wherein the first cap includes two conductive terminals that are insulated from each other, and one conductive terminal out of the two conductive terminals is disposed to be in electrical contact with the at least one anode flag group and other conductive terminal out of the two conductive terminals is disposed to be in electrical contact with the at least one cathode flag group.

8. The energy storage cell of claim 1, wherein the at least one anode flag group is separated from the at least one cathode flag group such that the at least one cathode flag group is accommodated in a first side and the at least one anode flag group is accommodated in a second side that is away from the first side.

9. The energy storage cell of claim 1, wherein the anode comprises a first flag group and a second flag group that are disposed at a flag distance, and the flag distance is a function of a thickness of the energy storage cell taken radially.

10. A method of manufacturing an energy storage cell, comprising: providing an anode with an anode active material excluding an anode uncoated portion; providing a cathode with a cathode active material excluding a cathode uncoated portion; and providing a separator configured to electrically isolate the anode and the cathode in a jelly roll structure of the energy storage cell; providing an anode flag group at the anode uncoated portion, the anode flag group being disposed towards a first longitudinal side of the energy storage cell; aligning the anode flag group with each other; providing a cathode flag group at the cathode uncoated portion, the cathode flag group being disposed towards the first longitudinal side of the energy storage cell; and aligning the cathode flag group with each other and separating the cathode flag group from the anode flag group.

11. The method of claim 10, further comprising: providing a cylindrical casing, wherein the cylindrical comprises a tubular body, a first cap and a second cap, wherein the first cap is disposed at the first longitudinal side to enclose the tubular body thereat and the second cap is disposed at a second longitudinal side to enclose the tubular body thereat.

12. The method of claim 11, further comprising: providing the first cap with two conductive terminals that are insulated from each other, and one conductive terminal out of the two conductive terminals is disposed to be in electrical contact with the anode flag group and other conductive terminal out of the two conductive terminals is disposed to be in electrical contact with the cathode flag group.

13. An electrode of an energy storage cell, comprising: a coated portion, wherein the coated portion is coated with an active electrode material; and an uncoated portion, wherein the uncoated portion comprises two or more flag groups provided on a first longitudinal side of the energy storage cell, the two or more flag groups are disposed at a group distance from each other, and the two or more flag groups are disposed to be in a first side when rolled into a jelly roll structure of the electrode.

14. The electrode of claim 13, the two or more flag groups each comprises a number of flags that are separated from each other at a flag distance and the number of flags extends outward in a longitudinal direction of the electrode such that the number of flags is oriented to align with each other in the jelly roll structure of the energy storage cell.

15. The electrode of claim 13, the two or more flag groups are disposed at the group distance from each other such that they are aligned to be within a substantial half-moon shape.

16. The electrode of claim 13, wherein the two or more flag groups are disposed at a fixed distance from each other.

17. The electrode of claim 13, wherein the two or more flag groups are disposed at a varied distance from each other.

18. The electrode of claim 13, the two or more flag groups are connectable to a current collector.

19. The electrode of claim 13, each flag of the two or more flag groups are configured to be at an angle of slanting with respect to a longitudinal axis of the electrode.

20. The electrode of claim 19, wherein the angle of slanting is in range of -60 to 60 degrees.