# Recent Advances in Lithiophilic Porous Framework toward Dendrite-Free Lithium Metal Anode
## 3 Non-Metal-Based Li Host
### Metal Oxides or Nitrides  
The overpotential during Li plating comes from (1) mass transfer, charge transfer, and ohmic resistance and (2) Li nucleation barrier. The mass transfer overpotential is related to the applied current density and the mobility of Li-ions, charge transfer and ohmic resistance depends on the electronic and/or ionic conductivity of the electrode and the ionic conductivity of the electrolyte. In contrast, the Li nucleation overpotential, which is the voltage difference between the bottom of the voltage dip and the latter voltage plateau depends on the energy barrier of Li nucleation. During the initial Li plating, the lithophilic metal oxides (such as ZnO and CuO) provide the Li nucleation side. The conversion and/or alloying reaction is beneficial for Li nucleation and excess storage of Li, which eventually lowers the nucleation overpotential and lowers the ultimate voltage hysteresis. For example, [PERSON] et al., decorated the bamboo-derived 3D hierarchical porous carbon (HPC) with ZnO quantum dots to confine up to 131 mAh cm\({}^{-2}\) lithium within its scaffold for stable LMA [10]. In the initial plating cycles, Li nucleates on the ZnO seeds with the conversion reaction. Figure 5: Lithiophilic behavior of heteroatoms and spared rGO. (**a,b**) Li nucleation voltage profile on various materials with some solubility and with negligible solubility at 10 \(\mu\)A cm\({}^{-2}\). Reproduced with permission from [83], Springer Nature, 2016. (**c**) Schematic illustration of Li plating/stripping behavior on a carbon nanofiber (CNF) with and without lithiophilic Sn. Reproduced with permission [88], American Chemical Society, 2019. (**d,e**) Core-level of N 1s XPS spectra in N-doped graphene and BE of Li atom with copper, graphene, and different functional groups of N-doped graphene. Reproduced with permission with [91], John Wiley and Sons, 2017. After higher plating cycles, the Li and Zn form the LiZn alloy. The Li nucleation is effectively controlled by both the lithiophilic ZnO seeds and LiZn alloy, resulting in smooth Li deposition as shown in Figure 6a,b. Moreover, lithiophilic gradient distributed ZnO particles on porous carbon against the Li-ion concentration gradient are supposed to reduce the lithium metal nucleation barrier [94]. The other form of lithiophilic material can be film or layer-type. The coating of the ZnO thin layer on the channel walls of 3D porous carbon by a simple and low-cost solution process method demonstrated a low overpotential of 90 mV and stable cycling performance 150 h at 3 mA cm\({}^{-2}\)[95]. The amorphous oxides show the superlithiophilic features owing to its higher binding energy (BE) compared to the crystallized oxides. [PERSON] et al., showed that the amorphous TiO\({}_{2}\) (\(-6.73\) eV) and SiO\({}_{2}\) (\(-2.20\) eV) have higher BE compared to the crystallized TiO\({}_{2}\) (\(-3.66\) eV) and SiO\({}_{2}\) (\(-1.97\) eV) [96]. The higher BE indicates the strong anchoring for Li adsorption and dense Li deposition. The SEM images after 100 cycles at 4 mA cm\({}^{-2}\) with a capacity of 1 mAh cm\({}^{-2}\) on Cu, 3D carbon fiber (CF), and 3D porous core-shell carbon fiber with amorphous SiO\({}_{2}\) and TiO\({}_{2}\) (PCSF) are shown in Figure 6c,d, Figure 6e,f, and Figure 6g,h, respectively. Only PCSF showed the uniform and smooth surface morphology of Li deposition indicating the strong anchoring behavior of lithiophilic SiO\({}_{2}\) and TiO\({}_{2}\). The PCSF demonstrated controlled Li plating, low nucleation overpotential, and low hysteresis. As a result, the symmetric cell test exhibited a stable Li plating/stripping of more than 350 cycles with a low overpotential of 35 mV at 4 mA cm\({}^{-2}\). The use of metallic nitrides as a lithiophilic seed has been demonstrated in the 3D porous carbon for significant improvement in the CE, stable symmetric cell, and full cell testing [97]. During initial Li nucleation, Mo\({}_{2}\)N converted to Mo and Li\({}_{3}\)N due to the highly reductive nature of Li.