Phospho-olivines are highly promising cathode materials for lithium-ion batteries. To overcome the low discharge voltage of LiFePO4 much attention has been paid to the partial substitution of iron by manganese and/or cobalt. In this work focused on lithiated mixed Fe-Mn-Co-B phosphates, we present the first study relative to the use of design of experiments for the optimization of battery active material composition. A good fit is obtained between experimental and adjusted values confirming the quality of the design. This methodology allows us to increase slightly the discharge capacity of LiFe(1-x-y-z)MnxCoyBzPO4 compounds. Additionally, cyclic voltammetry experiments indicate an improvement of lithium diffusion coefficient in LiFe0.333Mn0.667PO4 for both iron and manganese redox couples by addition of boron. (C) 2014 Elsevier B.V. All rights reserved.