NOVELTY - Electrochemical apparatus (E1), comprises: (a) aqueous electrolyte having many ions; (b) first electrode disposed in aqueous electrolyte, where the first electrode includes first Prussian blue analog material (I), the first Prussian blue analog material has first specific formula including a first cation P2 and a first cation R1, and the first Prussian blue analog material has first rate of electrochemical capacity loss when disposed in aqueous electrolyte; and (c) first conformal polymer layer disposed on first electrode, where the first conformal polymer layer is conductive to ions.    USE - The electrochemical apparatus is useful as a battery cell.    ADVANTAGE - The electrochemical apparatus exhibits decreased a rate of electrochemical capacity loss (claimed), thus extending a calendar life of the electrodes.    DETAILED DESCRIPTION - Electrochemical apparatus (E1), comprises: (a) an aqueous electrolyte having many ions; (b) a first electrode disposed in the aqueous electrolyte, where the first electrode includes a first Prussian blue analog material of formula (I), the first Prussian blue analog material has a first specific formula including a first cation P2 and a first cation R1, and the first Prussian blue analog material has a first rate of electrochemical capacity loss when disposed in the aqueous electrolyte; and (c) a first conformal polymer layer disposed on the first electrode, where the first conformal polymer layer is conductive to the ions. The first electrode with the first conformal polymer layer has a second rate of electrochemical loss less than the first rate of electrochemical capacity loss when the first electrode is disposed in the aqueous electrolyte.    A1 = cation;    P1 = metal cation;    R = transition metal cation;    B1 = CN;    L1 = ligand substitutable in the place of a CN- ligand;    j = 0-6;    x = 0-2;    y = 0-4;    z = 0-1; and    n = 0-5.    INDEPENDENT CLAIMS are also included for:    (1) an electrochemical apparatus (E2), comprising (a) as above per se, a first electrode disposed in the aqueous electrolyte, where the first electrode includes many nanoparticles of the first Prussian blue analog material (I), and each nanoparticle of the many nanoparticles includes an outside surface, and the first conformal polymer layer disposed on the outside surfaces, where the first electrode with the first conformal polymer layers disposed on the outside surfaces has a second rate of electrochemical loss less than the first rate of electrochemical capacity loss when the first electrode is disposed in the aqueous electrolyte;    (2) manufacturing the electrochemical apparatus including the first electrode having the first Prussian blue analog material (I), comprising (a1) forming the first conformal polymer layer on the first electrode, and (b1) disposing the first electrode in the aqueous electrolyte including the ions; and    (3) decreasing a rate of electrochemical capacity loss of a rechargeable energy storing electrochemical cell including an aqueous electrolyte having many ions, first electrode disposed in the aqueous electrolyte, and second electrode disposed in the aqueous electrolyte, comprising forming the first conformal polymer layer on the first electrode, forming a second conformal polymer layer on the second electrode, where the second conformal polymer layer is conductive to the ions, disposing the first electrode in the aqueous electrolyte including the ions, and disposing the second electrode in the aqueous electrolyte including the ions, where the first electrode with the first conformal polymer layer has a second rate of electrochemical loss less than the first rate of electrochemical capacity loss when the first electrode is disposed in the aqueous electrolyte, and the second electrode with the second conformal polymer layer has a fourth rate of electrochemical loss less than the third rate of electrochemical capacity loss when the second electrode is disposed in the aqueous electrolyte.