The present invention generally relates to carbophosphates and other compounds. Such compounds may be used in batteries and other electrochemical devices, or in other applications such as those described herein. One aspect of the invention is generally directed to carbophosphate compounds, i.e., compounds containing carbonate and phosphate ions. For example, according to one set of embodiments, the compound has a formula Ax(M)(PO4)a(CO3)b, where M comprises one or more cations. A may include one or more alkali metals, for example, lithium and/or sodium. In some cases, x is greater than about 0.1, a is between about 0.1 and about 5.1, and b is between about 0.1 and about 5.1. In certain embodiments, the compound may have a unit cell atomic arrangement that is isostructural to unit cells of the minerals sidorenkite, bonshtedtite, bradleyite, crawfordite, or ferrotychite. In some embodiments, the compound may have a formula Ax(M)(YO4)a(XO3)b, where A comprises one or more alkali metals, M comprises one or more cations, X includes B, C, and/or N, and Y includes Si, P, As, S, V, Nb, Mo, and/or W. In some cases, x is greater than about 0.1, a is between about 0.1 and about 5.1, and b is between about 0.1 and about 5.1. Other aspects of the invention are generally directed to techniques for making or using such compounds, kits involving such compounds, and the like.