Mass distribution indication of flow battery state of charge

1. An electrochemical device comprising: at least one electrochemical cell comprising an anode electrode and a cathode electrode; a reservoir configured to store an electrolyte; and a mass distribution measuring device comprising at least one of: a scale; a first pressure sensor located in a lower portion of the reservoir and a second pressure sensor located in an upper portion of the reservoir; or at least one strain gauge or load cell configured to measure a change in weight of the at least one electrochemical cell; wherein the electrochemical device is a flow battery; the at least one electrochemical cell comprises a stack of electrochemical cells; the electrochemical device further comprises a flow circuit connecting the stack of electrochemical cells and the reservoir; and at least one pump is located in the flow circuit, and the mass distribution measuring device is configured to measure one or more of a weight of the electrolyte in the reservoir, a weight of the reservoir, a pressure difference of the electrolyte across a given height of the electrolyte in the reservoir, or a weight of the stack of electrochemical cells; and a processor is configured to determine the state of charge based on output of the mass distribution measuring device.

2. An electrochemical device comprising: at least one electrochemical cell comprising an anode electrode and a cathode electrode; a reservoir configured to store an electrolyte; and a mass distribution measuring device comprising at least one of: a scale; a first pressure sensor located in a lower portion of the reservoir and a second pressure sensor located in an upper portion of the reservoir; or at least one strain gauge or load cell configured to measure a change in weight of the at least one electrochemical cell, wherein the mass distribution measuring device comprises the scale, and further comprises a flexible diaphragm which comprises at least a portion of a bottom surface of the reservoir, and the diaphragm is located between the scale and the electrolyte.

3. The electrochemical device of claim 2 , wherein the scale is configured to measure the weight of the electrolyte in the reservoir.

4. The electrochemical device of claim 2 , wherein the scale is configured to measure the weight of the reservoir.

5. An electrochemical device comprising: at least one electrochemical cell comprising an anode electrode and a cathode electrode; a reservoir configured to store an electrolyte; and a mass distribution measuring device comprising at least one of: a scale; a first pressure sensor located in a lower portion of the reservoir and a second pressure sensor located in an upper portion of the reservoir; or at least one strain gauge or load cell configured to measure a change in weight of the at least one electrochemical cell, wherein the mass distribution measuring device comprises the first pressure sensor located in a lower portion of the reservoir and the second pressure sensor located in an upper portion of the reservoir, and the mass distribution measuring device is configured to determine an average density of a fluid in the reservoir based on a pressure difference measured by the first and the second pressure sensors.

6. An electrochemical device comprising: at least one electrochemical cell comprising an anode electrode and a cathode electrode; a reservoir configured to store an electrolyte; and a mass distribution measuring device comprising at least one of: a scale; a first pressure sensor located in a lower portion of the reservoir and a second pressure sensor located in an upper portion of the reservoir; or at least one strain gauge or load cell configured to measure a change in weight of the at least one electrochemical cell, wherein the mass distribution measuring device comprises the at least one strain gauge or load cell configured to measure a change a weight of the at least one electrochemical cell, wherein: the at least one electrochemical cell comprises a stack of electrochemical flow battery cells; the electrochemical device further comprises electrolyte input and electrolyte output conduits connecting the stack and the reservoir; and the electrolyte input and electrolyte output conduits each comprise a bellow such that the electrolyte input and electrolyte output conduits bear substantially no weight of the stack.

7. The electrochemical device of claim 6 , wherein the at least one at least one strain gauge or load cell is located in one or more stack supports.

8. The electrochemical device of claim 1 , wherein the mass distribution measuring device is configured to measure the weight of the electrolyte in the reservoir.

9. The electrochemical device of claim 1 , wherein the mass distribution measuring device is configured to measure the weight of the reservoir.

10. The electrochemical device of claim 1 , wherein the mass distribution measuring device is configured to measure the pressure difference of the electrolyte across the given height of the electrolyte in the reservoir.

11. The electrochemical device of claim 1 , wherein the mass distribution measuring device is configured to measure or the weight of the stack of electrochemical cells.

12. The electrochemical device of claim 1 , wherein the mass distribution measuring device comprises the at least one load cell configured to measure the change in weight of the at least one electrochemical cell.

13. The electrochemical device of claim 6 , wherein the mass distribution measuring device comprises the at least one strain gauge configured to measure the change in weight of the at least one electrochemical cell.

14. The electrochemical device of claim 6 , wherein the mass distribution measuring device comprises the at least one load cell configured to measure the change in weight of the at least one electrochemical cell.