## 3 Results
### Strategies to Improve the Electrochemical Performance of the Investigated Samples  
#### 3.4.1 Incorporating Lithium in the HESO Lattice  
[PERSON] et al. [74] have recently evaluated the electrochemical performance of (MgCoNi-Zn)\({}_{1-x}\)Li\({}_{x}\)O, prepared by solid state reaction from milled MgO, CoO, NiO, ZnO, and Li\({}_{2}\)O oxides, as anode material in LIBs. They have reported that the incorporation of lithium in the HEO lattice generates oxygen vacancies (OVs) and the higher the OV concentration in the anode, the higher its specific capacity. In particular, (MgCoNiZn)\({}_{0.65}\)Li\({}_{0.35}\)O anode still delivers 610 mAh g\({}^{-1}\) after 130 cycles at 1 A g\({}^{-1}\)[74]. Here, a lithiated sample with nominal composition Li\({}_{1.8}\)(Cr\({}_{0.2}\)Mn\({}_{0.2}\)Fe\({}_{0.2}\)Co\({}_{0.2}\)Zn\({}_{0.2}\))\({}_{3}\)O\({}_{x}\), coded as LiSMF-sg, is produced by the SG route by adding Li salt to the same solution utilized to prepare sample 5 MF-sg. The incorporation of lithium in the HESO lattice leads to the formation of greater oxide particles (compare SEM, TEM and HRTEM images of samples 5 MF-sg and LiSMF-sg in Figures S8 and S9), without affecting the spatial distribution of the elemental constituents (Figure S9e), the oxide phase (compare XRD patterns of the two samples in Figure S10a) and its spatial uniformity, as evaluated by MRS (Figure S11). Nevertheless, by comparing the micro-Raman spectra of the samples (Figure S10b), some differences come into view. In Li5 MF-sg, a shoulder appears at 479 cm\({}^{-1}\), while the F\({}_{\rm 2g}\)(1) and A\({}_{\rm 1g}\) modes downshift (the apparent peak positions move from 189 and 654 cm\({}^{-1}\) to 181 and 634 cm\({}^{-1}\), respectively). Both these spectral changes are indicative of the generation of OVs induced by the incorporation of Li in the oxide lattice [75; 76; 77]. Figure 6 compares the electrochemical properties of anodes 5 MF-sg and Li5 MF-sg. Overall, CV and charge-discharge curves of Li\({}_{1.8}\)(Cr\({}_{0.2}\)Mn\({}_{0.2}\)Fe\({}_{0.2}\)Co\({}_{0.2}\)Zn\({}_{0.2}\))\({}_{3}\)O\({}_{\rm x}\) NPs (Figure 6b,d) do no not substantially differ from those of (Cr\({}_{0.2}\)Mn\({}_{0.2}\)Fe\({}_{0.2}\)Co\({}_{0.2}\)Zn\({}_{0.2}\))\({}_{3}\)O\({}_{4}\) NPs (Figure 6a,c), which is indicative of similar electrochemical processes. However, the strong reduction peak at the first cycle shifts to higher potential, and the peak intensity is stronger in the following cycles than that of 5 MF-sg, which could be caused by Li incorporation in the HESO lattice. As reported in literature [46], the electrochemical process can be tailored by the incorporation of different elements in high-entropy oxide structures. The initial lithiation/delithiation capacities of anode Li5 MF-sg (1112/733 mAh g\({}^{-1}\)) are slightly lower than for anode 5 MF-sg (1171/785 mAh g\({}^{-1}\)), probably due to the larger particle size. Nonetheless, the corresponding initial CE is higher (66% against 60.5%); this value is comparable to that reported for (FeCoNiCrMnZnLi)\({}_{3}\)O\({}_{4}\) prepared using the standard solid-state method (65%) [46]. Figure 6e,f compares the results of the rate capability test carried out on anodes 5 MF-sg and Li5 MF-sg. With increasing current densities, the capacities gradually decrease because of the increased electrode polarization. Compared with 5 MF-sg, Li5 MF-sg achieves larger capacities and superior rate capability. When tested at 20, 50, 100, 200, 500 and 1000 mA g\({}^{-1}\), the Li5 MF-sg electrode delivers good lithiation specific capacities of 702, 501, 388, 300, 213, 169 and 146 mAh g\({}^{-1}\), respectively. Additionally, when this sample is cycled at 500 mA g\({}^{-1}\) for 300 cycles (Figure 6g), a reversible capacity as high as 484 mAh g\({}^{-1}\) is  
Figure 6: Electrochemical performance of samples (**a,c,e**) 5 MF-sg, (**b,d,f**) Li5 MF-sg in Li-ion half cells.