TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The metal-ion secondary battery is formed by assembling a metal-ion or composite carbon cathode and the polymer electrolyte separator. Preferred Components: The polymer is: polymers comprising recurring units derived from MA monomer, from at least one per(halo)fluoromonomer including tetrafluoroethylene (TFE) and chlorotrifluoroethylene (CTFE), and from at least one hydrogenated co-monomer including ethylene, propylene and isobutylene, optionally containing one or more additional co-monomers, typically in amounts of 0.1-30 mol.%, based on the total amount of TFE and/or CTFE and the hydrogenated co-monomer(s); vinylidene fluoride (VDF) polymers comprising recurring units derived from the MA monomer, from VDF, and, optionally, from one or more fluorine-containing monomer(s) different from VDF. The VDF polymer comprises (a) at least 60 (preferably 85) mol.% of vinylidene fluoride (VDF); (b) optionally 0.1-15 (preferably 0.1-10) mol.% of a fluorinated co-monomer including vinylfluoride, CTFE, hexafluoropropene (HFP), TFE, trifluoroethylene and/or perfluoromethylvinylether; and (c) 0.05-10 (preferably 0.2-3) mol.% of the (meth)acrylic monomer. The (meth)acrylic monomer comprises acrylic acid-2-hydroxy-ethylester, acrylic acid-2-hydroxy-propylester and/or acrylic acid-2-hydroxy-1-methyl-ethyl ester. The metal compound complies with a structure of formula Ra4-m1-E(ORb)m1 or RA4-m2-E(ORB)m2. The mixture of step (i) further comprises at least one inorganic filler. The weight ratio between the liquid plasticizer and the polymer is at least 100 wt.%. The liquid plasticizer is present in an amount of 150-500 (preferably 350-500) wt.%. The electrolyte is M(PF6)n, M(BF4)n, M(ClO4)n, M(bis(oxalato)borate)n (M(BOB)n), M(N(CF3SO2)2)n, M(N(C2F5SO2)2)n, M(N(CF3SO2)(RFSO2))n, M(AsF6)n or M(C(CF3SO2)3)n.m1 = 1-4, preferably 1-3;E = Si, Ti and Zr;Ra, Rb = 1-18C hydrocarbon, optionally comprising one or more functional groups, where Ra and Raa are equal to or different from each other and at each occurrence;m2 = 2-3;RA = (1-12C)hydrocarbon, optionally comprising one or more functional group;RB = 1-5C linear or branched alkyl radical, preferably methyl or ethyl;RF = C2F5, C4F9, and CF3OCF2CF2; andM = Li, Na, K, and Cs; andn = 1-2. EXAMPLE - N-Methyl-2-pyrrolydone (NMP) (30 ml) and lithium perchlorate (0.65 g) were mixed under magnetic stirring at room temperature until complete dissolution occurred and a clear single phase solution of lithium perchlorate in NMP having a concentration equal to 0.2 M was obtained. Then VDF/HFP/hydroxyethylacrylate (HEA) copolymer (prepared by sequentially introducing demineralized water (2455 g) and Methocel K100 GR (RTM: Hydroxypropyl methylcellulose) suspending agent (0.63 g) in a reactor (4 l) equipped with an impeller running at a speed of 880 revolutions per minutes (rpm), venting and pressurizing the reactor with nitrogen to 1 bar, then introducing a solution of t-amyl perpivalate initiator (8.55 g) in isododecane into the reactor, followed by hexafluoropropene monomer (107 g) and vinylidene fluoride monomer (947 g), heating the reactor at 52 degrees C and a final pressure of 110 bar and then maintaining the temperature and pressure at 55 degrees C and at 110 bar respectively throughout the whole trial by feeding an aqueous solution of hydroxyethyl acrylate monomer (19.96 g/l), after 510 minutes, stopping the polymerization run by degassing the suspension until reaching atmospheric pressure, recovering the obtained polymer, and washing with demineralized water and oven-drying at 50 degrees C to obtain VDF/HFP/HEA copolymer (814 g)) (6 g) was added at room temperature. After the dissolution of the polymer was completed, slowly trickling tetraethylorthosilicate (6 g) and an aqueous hydrochloride solution (6 ml) in the solution under vigorous magnetic stirring. After mixing the mixture for 1 hour at 60 degrees C, a viscous liquid mixture was obtained. The liquid mixture was casted on a support plate with a Doctor Blade system, and solvent was removed at 80 degrees C under vacuum for 1 hour, to yield a self-standing polymer electrolyte separator.