NOVELTY - Substituted carbophosphate compounds (I) are new.    USE - (I) and (II) are useful: in electrodes used in electrochemical device (claimed) e.g. in a positive electrode within a battery or fuel cell; in lithium ion batteries or sodium batteries; and as a battery material (to store charge e.g. electronic charge) for power tools, hybrid electric vehicles, portable electronic devices and laptop computers.    ADVANTAGE - (I) and (II) are thermally stable and have higher energy densities.    DETAILED DESCRIPTION - Substituted carbophosphate compounds of formula (Ax(M)(PO4)a(CO3)b) (I) are new.    A = alkali metal;    M = non-alkali metal cation, where at least 25 mol.% of M comprises at least one non-alkali/non-alkaline earth metal;    x = greater than 0.1; and    a, b = 0.1-5.1    INDEPENDENT CLAIMS are also included for:    (1) a lithium-containing compound: having a unit cell atomic arrangement that is isostructural to a sidorenkite unit cell, a bonshtedtite unit cell, a bradleyite unit cell, a crawfordite unit cell or a ferrotychite unit cell; comprising at least 25 mol.% lithium, and unit cell containing carbonate triangular planar groups, phosphate tetrahedral groups and metal oxides of formula (M1O6) octahedral groups; and having an X-ray diffraction pattern (XRD) as given in the specification, where the XRD is acquired using an X-ray diffractometer having a copper kappa alpha source with a wavelength of 1.5418 Angstrom ;    (2) substituted metal compounds of formula (Ax(M)(Y1O4)a(XO3)b) (II);    (3) an electrochemical device comprising an electrode comprising (I) or (II); and    (4) preparation of (I).    M1 = positive cation;    X = B, C or N; and    Y1 = Si, P, As, S, V, Nb, Mo or W, where X and Y1 are in C and P, B and P, B and Si, C and Si, C and S, B and S, N and P, N and Si or N and S combinations respectively    Provided that: the composition does not include any of: Na, Al and Co, Si, N; Na, Fe, Si, B; Na, Al and Co, Si, C; Na, Mn, P, C; Na, Fe, P, C; Na, Co, P, B; Na, Mg and Fe, S, C; Na, Fe, S, C; Li, Cu, P, B; and Li, Zn, P, B combinations for A, M, Y1 and X, respectively; and when Y1 is V, Nb, Mo or W, then M is not V, Nb, Mo or W.