Papers comprising aerogel powder and aramid polymer fibrils

1. A paper suitable for use in a battery or battery pack as a flame barrier or thermal insulation, the paper comprising:

60 to 95 weight percent aerogel powder, and

5 to 40 weight aramid polymer fibrils;

the paper having a thickness of 50 to 4000 micrometers.

2. The paper of claim 1 further comprising mica, in an amount of 10 weight percent or more, based on the total weight of the aerogel powder, aramid polymer fibrils, and mica in the paper.

3. The paper of claim 2 , wherein the aramid polymer fibrils comprise poly (paraphenylene terephthalamide).

4. The paper of claim 3 wherein the aramid polymer fibrils comprise a blend of polymers, the blend of polymers comprising 80 to 96 weight percent poly (paraphenylene terephthalamide) and 4 to 20 weight percent of poly (vinyl pyrrolidone).

5. The paper of claim 2 having a thickness of 500 to 3000 micrometers.

6. The paper of claim 2 having a tensile strength of 0.5 to 100 MPa.

7. The paper of claim 2 having a thermal conductivity of 0.015 to 0.05 W/mK.

8. The paper of claim 1 , wherein the aramid polymer fibrils comprise poly (paraphenylene terephthalamide).

9. The paper of claim 8 wherein the aramid polymer fibrils comprise a blend of polymers, the blend of polymers comprising 80 to 96 weight percent poly (paraphenylene terephthalamide) and 4 to 20 weight percent of poly (vinyl pyrrolidone).

10. The paper of claim 1 having a thickness of 500 to 3000 micrometers.

11. The paper of claim 1 having a tensile strength of 0.5 to 100 MPa.

12. The paper of claim 1 having a thermal conductivity of 0.015 to 0.05 W/mK.

13. A battery cell, a battery module, or a battery pack comprising the paper of claim 1 .

14. A battery cell, a battery module, or a battery pack comprising the paper of claim 2 .