High entropy oxides for reversible energy storage

Abstract

In recent years, the concept of entropy stabilization of crystal structures in oxide systems has led to an increased research activity in the field of “high entropy oxides”. These compounds comprise the incorporation of multiple metal cations into single-phase crystal structures and interactions among the various metal cations leading to interesting novel and unexpected properties. Here, we report on the reversible lithium storage properties of the high entropy oxides, the underlying mechanisms governing these properties, and the influence of entropy stabilization on the electrochemical behavior. It is found that the stabilization effect of entropy brings significant benefits for the storage capacity retention of high entropy oxides and greatly improves the cycling stability. Additionally, it is observed that the electrochemical behavior of the high entropy oxides depends on each of the metal cations present, thus providing the opportunity to tailor the electrochemical properties by simply changing the elemental composition.

Gassing Behavior of High‐Entropy Oxide Anode and Oxyfluoride Cathode Probed Using Differential Electrochemical Mass Spectrometry

“…Selected charge/discharge curves and the lithiation capacities achieved over the first 100 cycles are shown in Figure . The results are in good agreement with previously published data . In recent years, it has been shown that the use of FEC instead of EC in LP57 electrolyte is beneficial to the long‐term cycling performance of especially alloying and conversion anode materials.…”

“…HEO was prepared by the NSP method . Mg(NO 3 ) 2 ⋅ 6H 2 O (Sigma Aldrich, 99.9 %), Zn(NO 3 ) 2 ⋅ 6H 2 O (Alfa Aesar, 99.9 %), Cu(NO 3 ) 2 ⋅ 2.5H 2 O (Sigma Aldrich, 99.9 %), Ni(NO 3 ) 2 ⋅ 6H 2 O (Sigma Aldrich, 99.9 %) and Co(NO 3 ) 2 ⋅ 6H 2 O (Sigma Aldrich, 99.9 %) served as precursors in the synthesis, with the final material forming in the gas phase of a hot‐wall reactor at 1150 °C and subsequent sintering at 1000 °C for 1 h …”

“…As mentioned previously, because the stable crystal structure of some of the oxides of the constituent elements is not of rock‐salt type (e. g., wurtzite ZnO or tenorite CuO), a certain enthalpy has to be overcome to allow formation of a single‐phase material . Recently, it has been shown that LIB cells using HEO as an anode active material are capable of delivering specific capacities of ≥600 mAh/g HEO over hundreds of cycles . Interestingly, extraction of a single cation species from the HEO led to not only a reduction in S config (1.39 vs 1.61 R) but also a significant decline in cycling stability, with the latter being reminiscent of common conversion anode materials .…”

“…Very recently, a new class of multicomponent electrode materials has been reported, which seems promising for the development of next‐generation LIBs . These materials exhibit tailorable properties and good cycling performance and belong to the so‐called high‐entropy oxides (HEOs).…”

“…Recently, it has been shown that LIB cells using HEO as an anode active material are capable of delivering specific capacities of ≥600 mAh/g HEO over hundreds of cycles . Interestingly, extraction of a single cation species from the HEO led to not only a reduction in S config (1.39 vs 1.61 R) but also a significant decline in cycling stability, with the latter being reminiscent of common conversion anode materials . Furthermore, each individual element apparently exerts some specific effect on the Li‐storage behavior (extraction of Cu led to a lower average lithiation potential while the respective compound without Zn revealed a two‐step oxidation process, for example), thereby paving the way toward a modular approach to electrode materials with tailored properties.…”