Reducing voltage hysteresis of metal oxide anodes to achieve high energy efficiency for Li-ion batteries
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 SnO 2 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 SnO 2 , SnO 2 -Mo, and 0.6 V in SnO 2 -P anodes is minimized to 0.3 V in a ternary SnO 2 -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 Fe 2 O 3 , Co 3 O 4 -basded conversion-type anodes. This work provides important guidance to advance the high-capacity metal oxide anodes from laboratory to industrialization.
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