Reducing voltage hysteresis of metal oxide anodes to achieve high energy efficiency for Li-ion batteries

Abstract

In the past two decades, a lot of high-capacity conversion-type metal oxides have been intensively studied as alternative anode materials for Li-ion batteries with higher energy density. Unfortunately, their large voltage hysteresis (0.8–1.2 V) within reversed conversion reactions results in huge round-trip inefficiencies and thus lower energy efficiency (50%–75%) in full cells than those with graphite anodes. This remains a long-term open question and has been the most serious drawback toward application of metal oxide anodes. Here we clarify the origins of voltage hysteresis in the typical SnO2 anode and propose a universal strategy to minimize it. With the established in situ phosphating to generate metal phosphates during reversed conversion reactions in synergy with boosted reaction kinetics by the added P and Mo, the huge voltage hysteresis of 0.9 V in SnO2, SnO2-Mo, and 0.6 V in SnO2-P anodes is minimized to 0.3 V in a ternary SnO2-Mo-P (SOMP) composite, along with stable high capacity of 936 mA h g−1 after 800 cycles. The small voltage hysteresis can remain stable even the SOMP anode operated at high current rate of 10 A g−1 and wide-range temperatures from 60 to −30 °C, resulting in a high energy efficiency of 88.5% in full cells. This effective strategy to minimize voltage hysteresis has also been demonstrated in Fe2O3, Co3O4-basded conversion-type anodes. This work provides important guidance to advance the high-capacity metal oxide anodes from laboratory to industrialization.