# Recent Advances in Lithiophilic Porous Framework toward Dendrite-Free Lithium Metal Anode
## 1 Introduction  
It has been challenging for lithium-ion batteries (LIBs) to meet the ever-increasing energy demands. The state-of-art LIBs, which are widely used in smart consumable electronics, energy-efficient plug-in-hybrid, and pure electric vehicles energy, are expected to reach the energy density of 300 Wh kg\({}^{-1}\) at the cell level [1; 2; 3]. However, the current market of LIBs has not yet reached a new goal set of 500 Wh kg\({}^{-1}\) or higher at the cell level for broad applications that require high energy density, high efficiency, and long life span. To reach such a high goal, Li metal has been regarded as a suitable alternative anode material, owing to its high theoretical capacity of 3860 mAh g\({}^{-1}\), low density of 0.59 g cm\({}^{-3}\), and low redox potential of \(-\)3.04 V versus standard hydrogen electrode (SHE) [4; 5]. Besides, lithium can involve aggressive chemistries approach such as operating at high voltage and/or pairing of the high capacity for the conversion-reaction in intercalation cathodes. For example, the Li metal anode (LMA) coupled with cathodes such as sulfur (S) and oxygen (O\({}_{2}\)), as next-generation lithium batteries, can offer splendidly high theoretical specific energy of 2567 Wh kg\({}^{-1}\) and 3505 Wh kg\({}^{-1}\), respectively [6]. However, Li anode raises lots of issues such as highly reactive nature with organic electrolytes,relatively infinite volume expansion during Li plating/stripping, uncontrolled dendrite formation that leads to low coulombic efficiency (CE) and safety concerns [7, 8]. Tremendous efforts have been made to realize the use of metallic Li as anode material in the battery, which includes (a) developing nano/microstructured Li host to accommodate the Li [8, 9, 10] and (b) ex-situ or in-situ derived solid electrolyte interphase (SEI) to shield the highly reactive Li metal from the liquid electrolyte [1, 2, 5, 11], (c) use of suitable solid-state electrolytes [12, 13], and (d) modification of separators [14, 15], etc. However, these result-oriented strategies are mainly concentrated on the dendrite-free Li deposition but less discusses the initial Li nucleation. Recently, the advanced technologies of employing a nano/microstructured Li host for dendrite-free Li deposition have attracted great attention. Three dimensional (3D) nano/microstructured Li host has a high surface area that lowers the local current density and allows a very thin and regular lithium coating, accommodates the volume expansion of Li within the structure and offers lower interfacial resistance [16]. However, most of the metal-based or carbon-based 3D nano/microstructured Li hosts are lithiophobic to the Li that leads to the poor Li wettability. As a result, the nucleation overpotential increases leading to high voltage hysteresis and unfavorable Li deposition. Thus, to increase the lithiophilicity of the porous materials, and spread the molten Li evenly, it is imperative to decorate the nano/microstructured Li host with the lithiophilic coating and/or heterogeneous seed growth. The lithiophilic nano-seeds, nanoparticles (NPs), or coatings can provide the initial nucleation site for guiding the uniform Li deposition densely and reversibly. This leads to a reduction in the voltage hysteresis, stability, and long battery cycling performance.  
In this review, the current fundamental understanding and key progress of lithiophilic nano/microstructured Li hosts are summarized. Furthermore, the issues, challenges, and a comprehensive viewpoint on the future development of lithiophilic nano/microstructured Li hosts are provided, aiming to boost the practical applications of LMA in high-energy-density batteries. The organized understanding of the formation of stable and robust SEI in lithium metal batteries (LMBs) can motivate designing the effective and efficient Li host in other battery systems.