After talking with Texas Instruments they gave me the following answer:
" The net tie It does connect Cell- to VSS, with this simple circuit there was likely not needed. In more complex designs it can be useful to keep multiple capacitors connected to VSS referencing the same potential of a high current trace such as Cell-. In this design the net tie could have been omitted."
I cannot understand why it could be usefull to keep multiple capacitors to VSS referencing the same potential of a high current trace such as Cell-
Could anyone explain this to me?