Reivindicaciones

1. Electrode for calcium batteries characterized in that the active electrode material is the calcium and vanadium oxide of formula Ca<x>V<2>O<4> wherein x is a value between 0 and 1. 2. Electrode according to claim 1, wherein the calcium and vanadium oxide is CaV<2>O<4>. 3. Electrode according to claim 1 or 2, wherein the electrode comprises electrically conductive additives selected from the list comprising: carbon, metals or ceramics. 4. Electrode according to any of claims 1 to 3, wherein the electrode comprises a polymer selected from the list comprising: polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), tetrafluoroethylenehexafluoropropylene copolymers, tetrafluoroethylenehexafluoropropylene copolymers (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFA), vinylidene fluoride-hexafluoropropylene copolymers, vinylidene, fluoride-chlorotrifluoroethylene copolymers, ethylenetetrafluoroethylene copolymers (ETFE resins), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymers, propylene-tetrafluoroethylene copolymers, ethylene-chlorotrifluoroethylene copolymers (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymers, ethylene-acrylic acid copolymers, and mixtures thereof 5. Electrode according to any of claims 1 to 4 wherein it is a positive electrode. 6. Method of manufacturing the electrode according to any of the preceding claims, comprising the following steps: - preparation of the oxide Ca<x>V<2>O<4>, wherein x is a value between 0 and 1, by reducing CaV<2>O<6>, and - deposition of the prepared oxide Ca<x>V<2>O<4> on a electrically conducting substrate. 7. Method according to claim 6 wherein the reduction step a) is carry out in the presence of a pure H<2>. 8. Method according to claim 7 wherein the reduction step is carried out at a temperature between 600 to 900°C for 2 to 8 hours. 9. A calcium-based secondary cell comprising: - a negative electrode - a positive electrode as defined in any of claims 1 to 5, - an electrolyte arranged between the negative electrode and the positive electrode, said electrolyte comprising a calcium salt. 10. Calcium-based secondary cell according to claim 9 wherein the negative electrode comprises graphite, carbon, meso-carbon microbead (MCMB), activated carbon, metallic calcium or a calcium alloy. 11. Calcium-based secondary cell according to claim 9 or 10 wherein the electrolyte is a solution of calcium tetrafluoroborate (Ca(BF<4>)<2>), calcium perchlorate (Ca(ClO<4>)<2>) calcium hexafluorophosphate (Ca(PF<6>)<2>), calcium tetrafluorosulfonylimide (Ca(TFSI)<2>) or (Ca(N(SO<2>CF<3>)<2>)<2>), calcium triflate Ca(Tf)2, calcium trifluoromethanesulfonate (Ca(CF<3>SO<3>)<2>) or mixtures thereof in an organic solvent. 12. Calcium-based secondary battery comprising an electrode as defined in claims 1-5 or a calcium-based secondary cell as described in claims 9-11. 13. Use of the oxide of formula formula Ca<x>V<2>O<4> ,wherein x is a value between 0 and 1, as an active electrode material. 14. Use of the oxide, according to claim 13, as an active positive electrode material of a calcium-based secondary battery. 15. Use of the electrode of any of claims 1 to 5 as part of a calcium-based secondary battery.