U.S. Patent  Jul.  17, 2018  Sheet 13 of 16  US 10,026,995 B2  FIG. 7  -+-Na/Na2C606-Conventional-Gravimetric  10000  ~--------------------- Na/Na2C606-conventional-Volumetric  ~Na/Na2C606-inventive-Gravimetric  -,+-Na/Na2C606-inventive-Volumetric  100  1000  Gravimetric energy (Wh/Kg) or Volumetric energy (Wh/l) 