## 6 Summary and Outlook  
The current state of the art on ZnFe\({}_{2}\)O\({}_{4}\) anode for LIBs demonstrates that they are very appealing materials thanks to their electrochemical features mainly related to the modification/choice of three peculiar aspects: (1) the particles' morphologies (downsizing the dimensions, obtaining nanowires, nanorods) by using synthetic routes such as co-precipitation, hydrothermal method, electrospinning, and using sacrificial template; (2) the formation of composites with carbonaceous materials (graphene, nanowires, nanotubes) or the proper coating of the particles to obtain exotic hybrid compounds with high porosity, and (3) the proper choice of the binder and electrolyte. The scaling down of the ZFO particle dimensions to nanoscale, the first cited factor, will increase the surface area, allowing access to the maximum number of reaction sites at the electrode-electrolyte interface and reducing the diffusion path length. In addition, the volume expansion during Li insertion is minimized with respect to the bulk form and the specific capacities' increase. However, the large surface area will lead to unwanted side reactions, which in turn produce the formation of a large amount of the SEI layer that degrades the capacity. The formation of  
Figure 10: (**a**) Rate capability and (**b**) long-term cycling stability and coulombic efficiency of ZFO/LFP-CNT full cells employing anodes with different degrees of lithiation [126]. Reproduced with permission, [PERSON] 2014.  
composites with carbonaceous materials, the second factor, can prevent the side reactions with electrode/electrolyte interface and accommodate volume strain. The core shell structure is the simplest strategy to enhance the electrochemical performance. The ZFO core can be covered by a shell consisting of amorphous carbon, which can act as a protection layer to strengthen the performance of core particles, by mainly avoiding the aggregation between the particles. In addition, the carbon shell with a proper thickness provides high electronic conductivity that enhances the lithium-ion diffusion rate. Another widely employed and winning strategy is the production by electrospinning of one-dimensional (1D) nanostructures, developing a well-interconnected conducting network, which can enhance the effective interaction between the active materials and electrolyte, shorten the diffusion length of the lithium ions and electrons, and buffer the strain energy, avoiding cracking and electrode pulverization. The third in-depth aspect concerns the binders. The widely used PVdF is progressively being substituted by CMC, PAA, and sodium alginate because they are more eco-friendly, less expensive, and able to completely cover the active material and accommodate the swelling of the electrode material. They also restrict the peeling of active material from the current collector, facilitating the tight attachment of the active material on the current collector and enhancing the electronic conductivity. These three crucial factors explain why, in the recently published papers, great efforts are devoted to synthesizing largely porous nanomaterials with morphologies able to support the huge volume changes during intercalation/deintercalation and to allow the electrolyte permeation. As demonstrated, very good cycling stability was obtained with high-capacity values for hundreds of cycles. The best results for ZFO are represented by some successful examples in which the use of templates, such as a metal organic framework or Prussian blue analogues as precursors to prepare porous and well-dispersed ZFO subunits in carbon matrix, allowed reaching capacities higher than 800 mAh g\({}^{-1}\) at 1 C for over 200 cycles. Hollow microspheres, too, obtained from the hydrothermal method guaranteed about 850 mAh g\({}^{-1}\) up to 20 C for 100 cycles, while one-dimensional nano-architecture with a polypyrrole shell can provide 880 mAh g\({}^{-1}\) at 1 C for 220 cycles.