Figure 3 (a) Schematic of the microstructure and fabrication process of the Lix M/graphene foils. (Reproduced from ref.[39], with permission from Copyright © 2017 Macmillan Publishers Limited, part of Springer Nature.) (b) Schematic representation of 3D Li-coated PI alloy electrode. (Reproduced from ref.[100], with permission from Copyright © 2016 Springer Nature.)

3.2 | Lithium alloys matrix Equations

By confining Li in a 3D structure, the infinite volume change during cycling could be eliminated[101]. Furthermore, the high surface area provided by 3D structures can further lower the localized current density and enable a more stable plating/stripping process[26]. Even confining the lithium metal in 3D carbon materials is a more common strategy, there are still some pioneering works on using the 3D lithium alloys matrix to host the lithium metal[26, 37, 102].
In 2014, Zhang’s group first employed a 3D lithium alloys (Li7B6) fibrous matrix for ultra-stable lithium-sulfur batteries[37]. The 3D nanostructured Li7B6 framework with high surface area and enough volume space, could not only decrease the areal current density, but also adequately accommodate the electrolyte and re-deposited Li to stabilize the concentration of Li ions. By employing this Li@Li7B6 anode, the Li-S batteries could stability cycle to 2000 cycles. Recently, Yan and his co-workers reported a 3D Mg doped LiB skeleton for hosting the metallic lithium and inhibiting the lithium dendrite growth as shown in Figure 4a and 4b [102]. The 3D LiB skeleton could significantly reduce volume variation during Li electrochemical dissolution/deposition process. Its superior lithiophilic and conductive characteristics could also contribute to the reduction of the local current density and homogenization of incoming Li+ flux. More importantly, Yan et al., used the Density Functional Theory (DFT) calculation proved the doping of Mg element to the 3D LiB skeleton could enhance the adsorption energy of Li. And the remaining Li-deficient Li-Mg alloy forming after Li stripped can help connect LiB fibers to stabilize the whole skeleton and lower interfacial resistance, which could effectively inhibit the lithium dendrite growth as shown in Figure 4c and 4d.