BATTERY CELLS BY SPIN CASTING

[0001] The present invention relates generally to a method and apparatus for

manufacturing battery cells and more specifically to a method and apparatus for manufacturing battery cells by spin casting and spin casted battery cells.

SUMMARY OF THE INVENTION

10002] A method of manufacturing a battery cell is provided that includes securing at least one end piece onto at least one end of a main portion of the battery cell, spinning the battery cell such that the at least one end piece revolves around an axis of the main portion and heating the at least one end piece during the spinning.

[0003] A method of manufacturing a battery cell is also provided that includes providing at least one end piece material onto at least one end of a main portion of the battery cell, spinning the battery cell such that the at least one end piece material revolves around an axis of the main portion and heating the at least one end piece material during the spinning to cure the end piece material into an end piece.

[0004] A spin molding apparatus is also provided. The spin molding apparatus includes a battery cell holding portion for securing a battery cell. The battery cell holding portion includes at least one heater for heating at least one end piece of the battery cell. The spin molding apparatus also includes a drive for rotating the cell holding portion about an axis of the cell holding portion. The drive rotates the cell holding portion about the axis of the cell holding portion such that at least one end piece of the battery cell revolves around an axis of a main portion of the battery cell.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The present invention is described below by reference to the following drawings, in which:

[0006] Fig. 1 shows a battery cell having molds mounted at ends thereof according to an embodiment of the present invention; [0007] Fig. 2 shows spin molding apparatus according to an embodiment of the present invention;

[0008] Fig. 3 shows a heater block of the spin molding apparatus according to an embodiment of the present invention;

[0009] Fig. 4 shows vertical struts of the spin molding apparatus according to an embodiment of the present invention;

[0010] Fig. 5 shows a shaft of the spin molding apparatus according to an embodiment of the present invention;

[0011] Fig. 6 shows the connection between a heater block, a strut and links of the spin molding apparatus according to an embodiment of the present invention;

[0012] Fig. 7 shows a detachable insulator of the spin molding apparatus according to an embodiment of the present invention;

[0013] Fig. 8 shows a detachable cooler of the spin molding apparatus according to an embodiment of the present invention;

[0014] Fig. 9 shows a bracket of the spin molding apparatus according to an embodiment of the present invention;

[0015] Fig. 10 shows a cut-away view of the arrangement of a Mercotac connector, a torque arm and the shaft of the spin molding apparatus according to an embodiment of the present invention;

[0016] Fig. 1 1 shows a cut-away view of the arrangement of pillow blocks, a timing belt pulley, the torque arm and the Mercotac connector with respect to one axial of the shaft according to an embodiment of the present invention;

[0017] Fig. 12 shows one of the molds according to an embodiment of the present invention; [0018] Fig, 13 shows one of the pillow block of the spin molding apparatus according to an embodiment of the present invention;

[0019] Fig. 14a shows one of the links of the spin molding apparatus according to an embodiment of the present invention;

[0020] Fig. 14b shows a side locking bar of the spin molding apparatus according to an embodiment of the present invention;

[0021] Fig. 15 shows a guard for the spin molding apparatus according to an embodiment of the present invention; and

[0022] Fig. 16 shows controls for the spin molding apparatus according to an

embodiment of the present invention.

DETAILED DESCRIPTION

[0023] Embodiments of the present invention use a spin casting method to make battery cells. The spin casting method may allow for broad scale and inexpensive production of battery cells and is compatible with rapid prototyping and mass customization objectives for the military. The spin casting method also has dual use potential, including for making rapid recharge batteries. The spin casting method may allow battery cells to be produced in approximately 5 minutes, while conventional methods take approximately 8 hours.

[0024] Fig. 1 shows a battery cell 10 in an intermediate form with a first mold 14a mounted on a first end of cell 10 and a second mold 14b, which is pulled back away from cell 10, for mounting on a second end of cell 10. In one preferred embodiment, battery cell 10 is a lithium ion battery cell. Molds 14a, 14b each retain an end piece 12 on the respective end of a main portion 16 of cell 10. Battery cell 10 is in an intermediate form because end pieces 12 are not yet permanently secured to main portion 16. In one preferred embodiment each end piece 12, before being permanently secured to main portion, is an end piece material in the form of a strip of molding compound having a consistency of putty that is loaded onto main portion 16. The molding compound may be formed of a polymer, which in one preferred embodiment is a thermoset polymer, most preferably thermoset polyester. Thermoset polyester may be selected based on its solvent resistance, adhesion to metals, low curing temperatures and cost. After one end piece 12 for example is loaded onto the first end of cell 10, mold 14a is placed over the end piece 12, and after another end piece 12 is loaded onto the second end of cell 10, mold 14b is placed over the end piece 12. In another preferred embodiment, end pieces 12 may be loaded into molds 14a, 14b before being loaded onto ends of main portion 16 and are held on the ends of main portion 16 by molds 14a, 14b. Each mold 14a, 14b may include two halves 18, 20. After molds 14a, 14b are secured on the ends of main portion 16, cell 10 is placed into a spin molding apparatus 30, as shown in Fig. 2, to heat end pieces 12, cure the molding compound and permanently secure end pieces 12 onto main portion 16.

[0025] Fig. 2 shows spin molding apparatus 30 according to one embodiment of the present invention. Spin molding apparatus 30 includes a battery cell holding portion 32 having two heater blocks 34a, 34b for contacting and heating respective molds 14a, 14b. Each heater block 34a, 34b includes a respective mold receiving portion 36 defined therein for receiving the respective mold 14a, 14b such that each heater block 34a, 34b surrounds one end piece 12, In one preferred embodiment, heater blocks 34a, 34b are formed as shown in Fig. 3. Heater blocks 34a, 34b are held together at the longitudinal ends thereof by vertical struts 38a, 38b, which are each coupled to respective axial sides 40a, 40b of a hollow shaft 40. In one preferred embodiment, struts 38a, 38b are formed as shown in Fig. 4. Heating blocks 34a, 34b may be electrically coupled to a power source by heating wiring 35 passing from heating blocks 34a, 34b into the inside of hollow shaft 40 via holes 37 in shaft 40, which is shown in Fig. 5 according to one preferred embodiment of the present invention.

[0026] In order to allow cell 10, with molds 14a, 14b mounted thereon, to be inserted into holding portion 32, either one of heater blocks 34a, 34b may be swung away from one of vertical struts 38a, 38b. A first hinge, which in the embodiment shown in Fig, 2 includes two hinge links 42a, may be provided to connect strut 38a and heater blocks 34a and to allow heater block 34a to be swung away from strut 38b. One preferred embodiment of the connection between heater block 34a, strut 38a and links 42a is shown in Fig. 6. A second hinge, which in the embodiment shown in Fig. 2 includes hinge links 42b, may be provided to connect strut 38b and heater block 34b and to allow heater block 34ab to be swung away from vertical strut 38a. Heater blocks 34a, 34b may include bore holes therein at the longitudinal ends thereof into which cap screws may be inserted to fix heater blocks 34a, 34b to vertical struts 38a, 38b. Four cross rods 46, two on each side of cell 10 when cell 10 is in holding portion 32, extending between vertical struts 38a, 38b contact faces of cell 10 to help secure cell in holding portion 32. Four side locking bars 47, two on each lateral side of cell 10 when cell 10 is in holding portion 32, may be provided in cell holding portion 32 for preventing lateral movement of cell 10 during the spin molding. As shown in Figs, 6 and 14b, side locking bars 47 may each include two bores holes 47a therein, each for receiving one of cross rods 46 such that side locking bars 47 each attached to two cross rods 46.

[0027] Shaft 40 is rotatably held in place on a base plate 50 by bearing pillow blocks 52, (one of pillow blocks 52 is shown in greater detail in Fig. 13), four of which are provided in the embodiment shown in Fig, 2. At least the outer pillow blocks 52 may each include a torque arm 53 attached thereto extending to the respective end of shaft 40. A timing belt drive 56 is provided on base plate 50 for rotating shaft 40 to spin battery cell holding portion 32 and the cell 10 retained therein about a central axis of shaft 40, as shown by arrow 58. Timing belt drive 56 includes a timing belt pulley 56a fixedly mounted on shaft 40, a timing belt 56b coupled to the circumference of pulley 56a for rotating pulley 56a and a DC motor 56c for driving timing belt 56b. Motor 56c is mounted on base plate 50 by a bracket 56b, which is shown in more detail in Fig. 9. In a preferred embodiment base plate 50 is formed as part of a heavy marble table to secure spin molding apparatus 30 and to resist the effects of vibration and imbalance that may be caused by the operation of spin molding apparatus 30.

[0028] A detachable insulator 60, one preferred embodiment of which is shown in Fig, 7, may be placed over each heater block 34a, 34b and held in place by quick release pins. In one preferred embodiment, insulator 60 may be formed of G-10 garolite and may include end plates 62, which may be stainless steel, having holes which quick release pins may pass through to removably fix insulator 60 on the respective heater block 34a, 34b. A cross-drilling in the holes permits a ball-detent at an end of each quick release pin to pop up and retain the pin (and insulator 60) in place.

[0029] After detachable insulators 60 are in place on heater blocks 34a, 36b and cell 10 is secured in cell holding portion 32, motor 56c is run up to speed for spinning battery cell 10 such that end pieces 12 revolve around an axis of main portion 16. Drive 56 rotates cell holding portion 32 about an axis of cell holding portion 32 such that end pieces 12 revolve around the axis of main portion 16. The actual RPM of the spin molding apparatus 30 may be checked by a tachometer (~ 500 RPM, which will generate around 10 g centripetal acceleration on the molding compound in end pieces 12) with a reflective target stuck to a strut, preferably on axial sides 40a, 40b of a shaft 40, and a sensor mounted on a leg of one of pillow blocks 52. Heater blocks 34a, 34b, which heat up quickly, are then turned on such that heater blocks 34a, 36b heat end pieces 12 during the spinning. In one preferred embodiment, each heater block 34a, 34b holds two 10 inch cartridge heaters, each rated at 725 watts. An appropriate temperature for rapid curing (~ 3 minutes) of the molding compound may be around 280 degrees Fahrenheit. Heater blocks 34a, 34b may be connected in series (inside of hollow shaft 40) and run on 220 VAC. Fig. 10 shows a cut-away view of the arrangement of a Mercotac connector 64, torque arm 53 and shaft 40 and Fig. 1 1 shows a cut-away portion of axial side 40a of shaft 40, showing the arrangement of pillow blocks 52, timing belt pulley 56a, torque arm 53 and a Mercotac connector 64 with respect to shaft 40. Mercotac connectors 64 may be provided inside of hollow shaft 40 at sides 40a, 40b of shaft 40 and may have rotating contacts for both power and for a thermocouple temperature sensor.

[0030] After about 2 to 4 minutes the molding compound of end pieces 12 sets and end pieces 12 are bonded to main portion 16. The spinning of cell holding portion 32 may then be stopped, heaters 34a, 34b are turned off and insulators 60 may be replaced with a detachable cooler, which in one preferred embodiment are finned aluminum heat sinks 66 as shown in Fig. 8. After finned aluminum heat sinks 66, which may be removably fixed to respective heater blocks 34a, 34b in the same manner insulators 60 are removably fixed to respective heater blocks 34a, 34b, are placed over heater blocks 34a, 34b, cell holding portion 32 may be spun again by drive 56 to cool down heater blocks 34a, 34b fairly quickly. Once fairly cool, spin molding apparatus 30 may be stopped to remove cell 10. Hinge links 42a, 42b, which as shown in greater detail in Fig. 14a, retain the hinged end of the respective heater block 34a, 34b, while allowing one or both of heating blocks 34a, 34b to be swung out of the way for removable of cell 10, In one preferred embodiment only one block 34a, 34b is moved to extract cell 10. Molds 14a, 14b may remain attached to cell 10 as cell 10 is removed from cell holding portion 32 and may then be pried off from cell 10 to exposed end pieces 12, which are securely attached to main portion 16 b the spinning of cell 10 in spin molding apparatus 10. As shown in Fig. 12, molds 14a, 14b may each have a line of vent holes 70 (— 1/16 inch diameter for example) running down the center split, which align with larger holes 72 (~ 1/8 inch diameter for example) in heater blocks 34a, 34b, as shown in Fig. 3, and holes 74 (~ 1/8 inch diameter for example) in insulators 60, as shown in Fig. 6. Holes 70, 72, 74 vent air and let the molding compound of end pieces 12 flow towards main portion 16. Any flashing of end pieces 12 may be trimmed off after molds 14a, 14b are removed.

[0031] In one alternative embodiment, the material used to form end pieces 12 may be provided in liquid form into molds 14a, 14b by an apparatus that is integral with, removable attachable to or separate from spin molding apparatus 30.

[0032] Since spin molding apparatus 30 poses a lethal hazard if parts fall off during spinning, a substantial guard 80, which is shown in Fig. 15, may be provided over spin molding apparatus 30 which may be easily swung out of the way for access to spin molding apparatus 30. In order to easily swing guard 80 for access, guard 80 may be supported by gas springs or struts. In one preferred embodiment, guard may be made of mild steel, which is for example 1/8 inch thick and painted or powder-coated finish. Lexan windows 82 may be provide on the sides guard 80 spin molding apparatus 30 operate when guard 80 is closed,

[0033] Fig. 16 shows one preferred embodiment of controls 90 for spin molding apparatus 30.

[0034] In the preceding specification, the invention has been described with reference to specific exemplary embodiments and examples thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner rather than a restrictive sense.