Li₈ZrO₆ as a Pre-lithiation Additive for Lithium-Ion Batteries

A major limitation of lithium-ion batteries is that 5–20% of lithium in the cathode is irreversibly lost on the anode surface during the first charge–discharge cycle. This reduces the capacity of the battery for the rest of its operating life. To compensate for the lithium loss, extra lithium can be added to the cathode prior to cell operation, a process called pre-lithiation. Li8ZrO6 (LZO) is lithium-rich with 8 Li+ per formula unit and can potentially provide a large number of lithium ions at relatively low mass loadings to compensate for the irreversible first-cycle capacity loss. LZO was evaluated as a pre-lithiation additive in combination with the cathode material LiNi0.5Mn1.5O4 (LNMO) and assembled in coin cells with graphite as an anode. Two forms of LZO were studied, one synthesized with intrinsic carbon (LZO/C) and one without intrinsic carbon. The fraction of LZO in the composites with LNMO was varied to determine the ratio providing the highest specific capacity per total mass of LNMO and LZO. For the same loading, the LZO additive without intrinsic carbon provided more lithium (5 Li+ per LZO or 550 mA h/g) than LZO/C (4 Li+ per LZO or 440 mA h/g) when charged to 4.8 V versus graphite. A loading of 5 wt % LZO was determined to be the optimal amount, delivering the largest number of Li ions with the smallest mass of the LZO additive, which resulted in 10–11% (on the basis of LNMO–LZO mass) or 15–18% (on the basis of LNMO mass) improved reversible specific capacity and 30% improved capacity retention for 50 charge–discharge cycles. Electrochemical impedance spectroscopy revealed that the combined contact and charge transfer resistance of an LNMO half-cell decreases significantly after prelithiation with LZO.