Solid electrolytes are highly important materials for improving safety, energy density, and reversibility of electrochemical energy storage batteries. However, it is a challenge to modulate the coordination structure of conducting ions, which limits the improvement of ionic conductivity and hampers further development of practical solid electrolytes. Here, we present a skeleton-retained cationic exchange approach to produce a high-performance solid electrolyte of Li ₃ Zr ₂ Si ₂ PO ₁₂ stemming from the NASICON-type superionic conductor of Na ₃ Zr ₂ Si ₂ PO ₁₂ . The introduced lithium ions stabilized in under-coordination structures are facilitated to pass through relatively large conduction bottlenecks inherited from the Na ₃ Zr ₂ Si ₂ PO ₁₂ precursor. The synthesized Li ₃ Zr ₂ Si ₂ PO ₁₂ achieves a low activation energy of 0.21 eV and a high ionic conductivity of 3.59 mS cm ⁻¹ at room temperature. Li ₃ Zr ₂ Si ₂ PO ₁₂ not only inherits the satisfactory air survivability from Na ₃ Zr ₂ Si ₂ PO ₁₂ but also exhibits excellent cyclic stability and rate capability when applied to solid-state batteries. The present study opens an innovative avenue to regulate cationic occupancy and make new materials.

Composite polymer electrolytes provide an emerging solution for new battery development by replacing liquid electrolytes, which are commonly complexes of polyethylene oxide (PEO) with ceramic fillers. However, the agglomeration of fillers and weak interaction restrict their conductivities. By contrast with the prevailing methods of blending preformed ceramic fillers within the polymer matrix, here we proposed an in situ synthesis method of SiO₂ nanoparticles in the PEO matrix. In this case, robust chemical interactions between SiO₂ nanoparticles, lithium salt and PEO chains were induced by the in situ non-hydrolytic sol gel process. The in situ synthesized nanocomposite polymer electrolyte delivered an impressive ionic conductivity of ~1.1 × 10⁻⁴ S cm⁻¹ at 30 °C, which is two orders of magnitude higher than that of the preformed synthesized composite polymer electrolyte. In addition, an extended electrochemical window of up to 5 V vs. Li/Li⁺ was achieved. The Li/nanocomposite polymer electrolyte/Li symmetric cell demonstrated a stable long-term cycling performance of over 700 h at 0.01–0.1 mA cm⁻² without short circuiting. The all-solid-state battery consisting of the nanocomposite polymer electrolyte, Li metal and LiFePO₄ provides a discharge capacity of 123.5 mAh g⁻¹, a Coulombic efficiency above 99% and a good capacity retention of 70% after 100 cycles.

Garnet Li₇La₃Zr₂O₁₂ is one of the most promising solid electrolytes used for solid-state lithium batteries. However, low ionic conductivity impedes its application. Herein, we report Ta-doping garnets with compositions of Li_7-xLa₃Zr_2-xTa_xO₁₂ (0.1 ≤ x ≤ 0.75) obtained by solid-state reaction and free sintering, which was facilitated by graphene oxide (GO). Furthermore, to optimize Li_6.6La₃Zr_1.6Ta_0.4O₁₂, Mg²⁺ was select as a second dopant. The dual substitution of Ta⁵⁺ for Zr⁴⁺ and Mg²⁺ for Li⁺ with a composition of Li_6.5Mg_0.05La₃Zr_1.6Ta_0.4O₁₂ showed an enhanced total ionic conductivity of 6.1 × 10⁻⁴ S cm⁻¹ at room temperature. Additionally, spark plasma sintering (SPS) was applied to further densify the garnets and enhance their ionic conductivities. Both SPS specimens present higher conductivities than those produced by the conventional free sintering. At room temperature, the highest ionic conductivity of Li_6.5Mg_0.05La₃Zr_1.6Ta_0.4O₁₂ sintered at 1000 °C is 8.8 × 10⁻⁴ S cm⁻¹, and that of Li_6.6La₃Zr_1.6Ta_0.4O₁₂ sintered at 1050 °C is 1.18 × 10⁻³ S cm⁻¹.