NASICON-Structured LiGe₂(PO₄)₃ with Improved Cyclability for High-Performance Lithium Batteries

LiGe 2 (PO 4 ) 3 (LGP) with a NASICON structure is synthesized through the solid state method. Well-crystallized LGP obtained at 900 °C shows a total lithium (Li) ion conductivity of 7.2 × 10 −7 S/cm. For the first time, the Li reversible capability of bulk LGP is measured to be 460 mAh/g at a charge rate of 150 mA/g in the voltage range from 0.001 to 1.5 V. Very good capacity retention of 92% after 25 cycles is achieved in comparison to 28% of GeO 2 . At a very high charge rate of 1500 mA/g the LGP reveals excellent capacity retention of 77% after 1000 cycles. The average discharge and charge plateau is in the range from 0 to 0.4 V vs. Li. Mechanisms for the improved cycling performance of the LGP in comparison with GeO 2 are discussed, suggesting that Li 3 PO 3 acts as a more stable and conductive inactive matrix to buffer volume expansion during Li alloying. Our results may suggest a direction to design better material systems with a combination of active and inactive materials.