In wireless rechargeable sensor networks (WRSN), rechargeable sensor nodes harvest ambient RF energy from power sources such as the RFID readers. However, the simultaneous transmissions may cause severe communication collisions. Different from traditional approaches which mainly resolve such collisions at the MAC layer, in this work we optimize the deployment of RFID reader in order to avoid the communication collisions by exploiting the differences in the time of charge among rechargeable sensor nodes. Specifically, when the reader is able to cover the whole deployment field, an efficient collision-free solution with proved optimality is presented to minimize the communication delay in the network. Simulation results are employed to verify the proposed algorithm.