Synergized Tricomponent All‐Inorganics Solid Electrolyte for Highly Stable Solid‐State Li‐Ion Batteries

Garnet‐type oxide Li(6.4)La(3)Zr(1.4)Ta(0.6)O(12) (LLZTO) features superior ionic conductivity and good stability toward lithium (Li) metal, but requires high‐temperature sintering (≈1200 °C) that induces high fabrication cost, poor mechanical processability, and high interface resistance. Here, a novel high‐performance tricomponent composite solid electrolyte (CSE) comprising LLZTO−4LiBH(4)/xLi(3)BN(2)H(8) is reported, which is prepared by ball milling the LLZTO−4LiBH(4) mixture followed by hand milling with Li(3)BN(2)H(8). Green pellets fabricated by heating the cold‐pressed CSE powders at 120 °C offer ultrafast room‐temperature ionic conductivity (≈1.73 × 10(−3) S cm(−1) at 30 °C) and ultrahigh Li‐ion transference number (≈0.9999), which enable the Li|Li symmetrical cells to cycle over 1600 h at 30 °C with only 30 mV of overpotential. Moreover, the Li|CSE|TiS(2) full cells deliver 201 mAh g(−1) of capacity with long cyclability. These outstanding performances are due to the low open porosity in the electrolyte pellets as well as the high intrinsic ionic conductivity and easy deformability of Li(3)BN(2)H(8).