[0001] The invention relates to a positive electrode that includes the calcium and manganese oxide of formula Ca<2>MnO<3.5> as positive-electrode active material and its manufacturing method. The invention also relates to a calcium-based secondary cell comprising said electrode and to a calcium-based secondary battery comprising such a calcium-based secondary cell.
1. Electrode, for calcium-based secondary battery characterized in that the active electrode material is the calcium and manganese oxide of formula Ca<2>MnO<3.5>. 2. Electrode, according to claim 1, wherein the electrode comprises electrically conductive additives selected from the list comprising: carbon, metals or ceramics. 3. Electrode, according to claim 1 or 2, 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. 4. Electrode, according to any of claims 1 to 3, wherein it is a positive electrode. 5. Method of manufacturing the electrode according to any of the preceding claims, comprising the following steps: - preparation of the oxide Ca<2>MnO<3.5> by reducing Ca<2>MnO<4>, and - deposition of the prepared oxide Ca<2>MnO<3.5> on an electrically conducting substrate. 6. Method, according to claim 5, wherein the reduction of Ca<2>MnO<4> is carry out in the presence of a NH<3> flow between 50 and 1200 ml/min. 7. Method, according to any of claims 5 to 6, wherein the reduction of Ca<2>MnO<4> is carry out at a temperature between 390 and 550°C. 8. Method, according to any of claims 5 to 7, wherein the reduction of Ca<2>MnO<4> is carry out in during a time in the range 4h to 50h. 9. A calcium-based secondary cell comprising: - a negative electrode, - a positive electrode as defined in any of claims 1 to 4 and - 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 any of claims 8 to 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 1-4 or a calcium-based secondary cell as described in claims 9-11. 13. Use of the oxide Ca<2>MnO<3.5> as an active electrode material. 14. Use of the oxide Ca<2>MnO<3.5>, 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 4 as part of a calcium-based secondary battery.