Among various anode materials for lithium-ion batteries (LIBs), conversion alloyed metal oxides (or sulfides) have attracted much attention due to their high theoretical capacities. However, the volume expansion of active metals during alloying can lead to irreversible transformation reactions. Heterostructured anodes designed through the coupling of metal oxides and sulfides have abundant interfaces that facilitate electron transfer and improve surface reaction kinetics, but the interfacial effect mechanism to improve their rate and cycling performance has not been deeply studied.

Figure 1. Design, synthesis and characterization of ZnO/ZnS heterostructures

 

Here, Prof. Fuqiang Huang and Associate Prof. Guobao Li of Peking University, et al. utilized the in-situ partial conversion of metal sulfides to oxides with high lattice matching to design ZnO/ZnS heterostructures to understand the effect of the interface on the large capacity and high performance of LIB anodes. The effect of reversible Li storage. Specifically, the authors first used zinc acetate (ZnAc2) as the zinc source, sublimated sulfur powder as the sulfur source, and polyethylene glycol (PEG) as the auxiliary material to prepare the ZnS:OH precursor. Then, ZnS:OH nanodots were annealed at 600 °C under Ar atmosphere to prepare ZnO/ZnS heterostructures. Benefiting from the fast interfacial Li transport and reaction kinetics, the ZnO/ZnS interface can be transformed into uniform ZnOxS1-x nanodots through repeated cycling. DFT calculations show that zinc oxysulfide has an optimized Li adsorption performance to accelerate the electrode reaction. Meanwhile, the integration of the resulting Li2O/Li2S substrate with LiZn nanodots provides more Li+ anchoring sites and alters the charge redistribution, thereby facilitating interfacial Li storage.

Figure 2. Theoretical calculation of Li adsorption at the ZnO/ZnS anode interface

 

Therefore, the ZnO/ZnS heterostructure provides a capacity of 1213 mAh g-1 after 100 cycles at 0.1 A g-1, and the capacity remains 920 mAh g-1 even after 1300 cycles at 2 A g-1, This suggests that ZnO/ZnS is a promising alternative anode for high energy/power density LIBs. In addition, the assembled coin-type full cell with ZnO/ZnS anode and high-voltage (4.5 V) LiCoO2 cathode can reach a maximum energy density of about 285 Wh kg-1 and still achieve a capacity of 84.8 mAh g-1 after 200 cycles at 2 C 1, corresponding to a capacity retention rate of 81.9 %. Even, the pouch cell based on ZnO/ZnS anode provides a capacity of 103.5 mAh at 2 C and maintains 88.4 mAh (85.4% capacity retention) after 300 cycles. Therefore, such button-type and pouch full cells further show excellent electrode stability and compatibility. In conclusion, this study sheds light on phase reconfiguration and potential interfacial Li storage mechanisms in heterostructured anodes, and opens up new avenues for designing high-capacity anodes for LIBs.

 

Figure 3. Electrochemical performance of button and pouch full cells

Quote: Interfacial lithium absorption enhanced ZnO/ZnS heterostructure for robust and large-capacity energy storage, Energy & Environmental Science 2022. DOI: 10.1039/D2EE00050D