Mi 4C stuck on preparing apps boot loop

[BeardedBert]

Hi,

years ago i installed the Teamsuperluminal's CM13 on my Xiaomi Mi 4c and it it worked for a long time without major issues. Lately the phone started to auto power down when the battery reached appr. 50% charge. I would hook it up to a charger and reboot it and charge it back up again. Then it was fine again, this has been going on for months now. But yesterday it auto powered down again and after reboot it showed the CM boot logo for an unusual amount of time, after that it started preparing apps for start. When it was done with that it would just immediately reboot and start over again. So it is now stuck on a preparing apps reboot loop.

What i have tried so far:
1. Wipe cache and dalvik in TWRP and reboot. Didn't help
2. Tried to reformat a partition that might be corrupted due to brown out with:

make_ext4fs /dev/block/mmcblk0p15

It shows the following error:

Creating filesystem with parameters:
    Size: 131072
    Block size: 4096
    Blocks per group: 32768
    Inodes per group: 16
    Inode size: 256
    Journal blocks:1024
    Label:
    Blocks: 32
    Block groups: 1
    Reserved block group size: 7
error: ext4_allocate_best_fit_partial: failed to allocate 1005 blocks, out of space?

But there are more than 2GB of free space available and mmblk0p15 is then missing from /dev/block/ , so if i run the same command again i get:

Need size of filesystem

How can i repair this or what log file might be interesting?