Ultrahigh-voltage LiCoO 2 at 4.7 V by Interface Stabilization and Band Structure Modification.

Lithium cobalt oxide (LCO) is widely used in lithium-ion batteries for portable devices due to its high volumetric energy density, which is generally charged to 4.3 V. If the cut-off voltage of LCO is lifted from 4.3 V to 4.7 V, the specific capacity of LCO will increase from 150 to 230 mAh g -1 with a significant improvement of 53%. However, LCO suffers serious problems of H1-3/O1 phase transformation, unstable interface between cathode and electrolyte, and irreversible oxygen redox reaction at 4.7 V. Herein, interface stabilization and band structure modification are proposed to strengthen the crystal structure of LCO for stable cycling of LCO at an ultrahigh voltage of 4.7 V. Gradient distribution of magnesium and uniform doping of nickel in Li layers effectively inhibit the harmful phase transition of LCO, while uniform LiMg x Ni 1-x PO 4 coating on LCO surface stabilizes the LCO-electrolyte interface to prevent electrolyte decomposition and cobalt dissolution under high delithiation states. Moreover, the decreased band gap improves the electrochemical performance of the modified LCO, and the charge compensation of nickel and phosphorus and fewer electrons occupying the O 2p antibonding orbitals jointly suppress oxygen charge deficiency and improve oxygen redox reaction reversibility. As a result, the modified LCO has a high capacity retention of 78% after 200 cycles at 4.7 V in a half cell and 63% after 500 cycles at 4.6 V in a full cell. This work makes the capacity of LCO one step closer to its theoretical specific capacity. This article is protected by copyright. All rights reserved.