Frame for an electrochemical energy-storage unit

Abstract

The present invention relates to a process for producing frame elements for a frame for holding and arranging electrochemical cells in an electrochemical energy-storage unit. The present invention also relates to the use of certain plastics mixtures for producing said frame elements. The frame elements or frames of the invention are particularly preferably used in electrochemical energy-storage units with high power density. Electrochemical energy-storage units of this type with high power density are more particularly used for the operation of motor vehicles with electrical drive, for example in vehicles which are driven on the “hybrid” principle (electrical drive and internal combustion engine), and are also preferably used for exclusively or primarily electrically operated vehicles. It is preferable here to use, as electrochemical energy-storage units with high power density, lithium-ion batteries or lithium-polymer batteries.

Claims

1. A method for the manufacturing frame elements for frames for electrochemical energy storage units, wherein the method comprises the following steps: (i) providing a polymer selected from the group consisting of a homopolymer, a copolymer, and mixtures thereof; (ii) adding to the polymer at least one additive selected from the group consisting of softeners, flame retardants, processing aids, and elastomer modifiers to obtain a polymer blend; (iii) injection molding the polymer blend to manufacture a frame element, wherein the polymer blend has a specific thermal conductivity of more than 1 W/(m K), wherein the polymer blend obtained in step (ii) includes (a) mixtures of PC, PP, PBT, and PET with elastomer modified phases, and (b) mixtures (blends or polymer alloys) comprising PA6/PA66 blends with 10 to 40% PA66, PA6/PA66/PA12 tri-blends, PA6/PA1010 blends, PA6/PA12 blends, or PA1010/PA12 blends, wherein the frame element has a specific resistance of more than 1 Ωm (at 20° C.).

2. The method as claimed in claim 1, wherein the HDT/B value of the frame element is 50° C. to 200° C. (ISO 75).

3. The method as claimed in claim 1, wherein an elastomer is added to the polymer during step (ii).

4. The method as claimed in claim 1, wherein the homopolymer of step (i) is selected from the group consisting of polyamide (PA), thermoplastic polyurethane (PU), polyester, polyoxymethylene (POM), polyphenylene oxide (PPO), polyphenyl sulfide (PPS), polyimide (PI), and polybutylene terephthalate (PBT).

5. The method as claimed in claim 1, wherein the copolymer of step (i) is selected from the group consisting of PA 6/12, PA 66/6, PA 66/610 or PA 12/6/66 copolymers, wherein the PA 66/6 copolymers include copolymers where the polyamide is polymerized by the simultaneous polycondensation of PA66 and PA6 blocks, with the ratio of the PA66 blocks being in the range of 10 to 80% by weight.

6. The method as claimed in claim 1, wherein the polymer blends obtained in step (ii) include mixtures (blends or polymer alloys) comprising PA6/PA66 blends with 10 to 40% PA66, PA6/PA66/PA12 tri-blends, PA6/PA1010 blends, PA6/PA12 blends, or PA1010/PA12 blends.

7. The method as claimed in claim 1, wherein the at least one homopolymer or the at least one copolymer or the mixture of these contains at least one elastomer-modified polyamide.

8. The method as claimed in claim 1, wherein the at least one homopolymer or the at least one copolymer or the mixture of these contains at least one block copolymer.

9. The method as claimed in claim 1, wherein the at least one homopolymer or the at least one copolymer or the mixture of these contains mixtures of PA/polyethylene blends, blends of PA6, PA12 or PA66 with polyphenyl ether, PA/ABS blends, PA/polyphenylene sulfide blends, or PA6/PET blends.

10. The method as claimed in claim 1, wherein the at least one homopolymer or the at least one copolymer or the mixture of these contains PC/ABS blends, PC/PE blends, PC/PET blends or PC/PS blends.

11. The method as claimed in claim 1, wherein the electrochemical energy storage unit includes a lithium-ion battery.

12. The method as claimed in claim 1, wherein the electrochemical energy storage unit has a power density of more than 100 W/kg.

13. The method as claimed in claim 1, wherein the frame element is electrically non-conducting or badly conducting and preferably has a specific resistance of more than 10.sup.20 Ωm (at 20° C.).

14. The method as claimed in claim 1, wherein the HDT/B value of the frame element is 80° C. to 200° C. (ISO 75).

15. The method as claimed in claim 1, wherein the electrochemical energy storage unit has a power density of more than 2000 W/kg.

16. The method as claimed in claim 1, wherein the polymer in step (i) is a PA6/PA66 polymer blend or copolymer with 25 to 35% PA66.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts a frame element according to an embodiment of the application.

(2) FIG. 2 depicts a thermogravimetric analysis (TGA) of a frame element according to an embodiment of the application.

(3) Example of an Application

(4) For the example of the polymer blend Grilon TS V0 (a polymer blend containing PA6 and PA6.6), it is shown below that frame elements made by means of the method according to the invention fulfill in a particular way the requirements for electrochemical energy storage units with high power density.

(5) 1. Dimensional Stability Under Heat/Flammability

(6) If during short term heat exposure a certain temperature limit is exceeded, the intermolecular forces between the polymer chains are reduced, the molecule chains slip more easily past each other and the thermoplastic material starts flowing. In order to investigate the dimensional stability under heat, a test battery was made. For this, instead of Li-ion cells, metal plates of the same weight (330 g) were clamped into the frame elements. This test setup was then placed into an oven onto two bars for over 24 hours at 90° C. in order to test the dimensional stability under heat.

(7) By means of comparing the dimensions before and after the 24 hours, it could be determined that the frame continued to be stable and had not warped.

(8) In addition, it was found during a flammability test that the frame elements made according to the invention will eventually melt if exposed to the flame of a Bunsen burner, but they will not burn. In particular, no burning drops fall off.

(9) 2. Strength Test

(10) The strength of the frame was investigated using the Dynstat method. The Dynstat method is advantageous, because small sample sizes (such as length=15±1, width=10±0.5 and thickness 1.2 to 4.5 mm) can be taken from the workpiece and tested. In this way samples can be made even from complex components which have no large, level surfaces.

(11) FIG. 1 shows a frame element made using the method according to the invention for an electrochemical cell (material: the PA6 and PA6.6 polymer blend mentioned above). FIG. 1 also shows the location of the samples in the frame. The upper three samples are located perpendicular to the flow direction and the lower three samples in parallel to the flow direction.

(12) Here the following values for the impact strength (first table) and the flexural strength (second table) were found (n.f.—no failure):

(13) TABLE-US-00002 Width Thickness A.sub.n a.sub.n Sample No. [mm] [mm] [kpcm] [kJ/m.sup.2] orientation 1 10.07 1.58 — n.f. parallel 2 10.08 1.50 — n.f. parallel 3 10.10 1.59 — n.f. parallel 4 10.03 1.49 — n.f. parallel 5 10.14 1.51 — n.f. parallel 6 10.04 1.48 — n.f. perpendicular 7 10.09 1.50 — n.f. perpendicular 8 10.14 1.52 — n.f. perpendicular 9 10.30 1.45 — n.f. perpendicular 10 10.01 1.49 — n.f. perpendicular

(14) TABLE-US-00003 Width Thickness M Sample No. [mm] [mm] [kpcm] [N/mm.sup.2] orientation 1 10.16 1.44 3.1 86.6 parallel 2 10.06 1.44 3.2 86.5 parallel 3 10.12 1.52 3.3 93.1 parallel 4 10.08 1.55 3.4 90.0 parallel 5 10.10 1.49 3.4 89.2 parallel 6 10.13 1.55 3.2 82.5 perpendicular 7 10.08 1.58 3.2 80.6 perpendicular 8 10.08 1.47 3.4 82.6 perpendicular 9 10.15 1.50 3.5 84.6 perpendicular 10 10.02 1.49 3.3 77.2 perpendicular

(15) TABLE-US-00004 Statistics Sample body total Parallel Perpendicular n 10 5 5 x 85.29 89.08 81.50 s 4.77 2.73 2.79 v 5.59 3.07 3.42

(16) These measurements show therefore that the polymer blend according to the present invention is particularly suitable for the electrochemical energy storage devices.

(17) 3. Investigation of Aging

(18) Here the durability of the activation energy of the frame elements was investigated.

(19) The aging of the polymer of the frame was computed based on an investigation by means of thermogravimetric analysis (TGA). For this only the influence of thermal aging was investigated. Other influences, such as the influences from the environment, UV light etc. were ignored.

(20) The TGA was carried out with four different heating rates (5, 10, 15 and 20 K/min) exposed to air with a sample size of about 10 mg. FIG. 2 shows the four TGA curves.

(21) From the TGA curves, two points of inflection can be determined. The first is between 300 and 350° C., the second between 400 and 470° C.

(22) In the area of the first point of inflection there is a weight loss of between 9 and 15%, at the second the loss is between 40 and 70%.

(23) TABLE-US-00005 Point of inflection of the weight change 1 2 Decomposition 300 to 350 400 to 470 temperature [° C.] Weight loss [%] approx. 9 to 12 approx. 40 to 70

(24) Up to a weight loss of approx. 10 to 12% the mechanical properties do not seriously change, so the plastic material Grilon TS V0 in the deployment range from 40 to 60° C. can be used with advantage for frame elements in electrochemical energy storage units, even if cells held in the frame warm up significantly. This is particularly relevant as the available tests also indicate suitability as frame elements for electrochemical energy storage units when the cells to be supported by the frame are relatively heavy and are prone to release heat energy.

(25) The durability is calculated from the kinetic equation (based on Arrhenius' equation) for the thermal decomposition reaction, and these results are used to calculate the service life as is shown in the table below.

(26) By means of the TGA curves, the relationship between temperature and weight loss can be determined. From this, the activation energy can be calculated. For the Grilon ST V0 polymer blend it is 101.617 kJ/mol. By means of the activation energy the durability of the polymer can be determined for any operating temperature:

(27) TABLE-US-00006 Service life t.sub.f [years] Operating temperature [° C.] 90.26 40 48.88 45 26.97 50 15.16 55 8.67 60 5.04 65 2.98 70 1.78 75 1.09 80 0.67 85 0.42 90 0.26 95 0.17 100

(28) A service life of more than eight for a temperature of 60° C. is to be regarded as advantageous for the intended application.