Conceptual design for 12 V lead-free accumulators is presented using basic research results on lithium insertion materials. Among possible materials, Li[Li1/3Ti5/3]O-4 is selected for a negative-electrode material, and Li[Ni1/2Mn3/2]O-4, LiMn2O4, LiCo1/3Ni1/3Mn1/3O2, and LiFePO4 are specifically considered as positive-electrode materials. Combination of these materials with Li[Li1/3Ti5/3]O-4 gives a 2,2.5 or 3 V lithium-ion battery. Series connection of such a lithium-ion battery makes 12 V lead-free accumulators possible. Characteristic features of the lead-free accumulators are discussed in terms of energy density for deep charge and discharge cycles, power density for short period of time, material economy, environmental friendliness, and safety compared with those of lead-acid batteries currently hold a position in automobile, large uninterruptible power supply, and off-grid solar home systems. (C) 2007 Elsevier B.V. All rights reserved.