Synergic Titanium Nitride Coating and Titanium Doping by Atomic Layer Deposition for Stable- and High-Performance LiFePO₄

Atomic layer deposition (ALD) method has emerged as a promising technique to address the dissolution and poor conductivity of electrode materials of lithium ion batteries. In this work, surface modification of LiFePO4 (LFP) was carried out by titanium nitride (TiN) ALD, during which a Ti doping into LFP occurred simultaneously. X-ray photoelectron spectroscopy (XPS) and electrochemical tests were performed to prove the Ti doping, and the composition of TiN layer on the surface of LFP particles was interpreted as a combination of TiN and titanium oxynitride (TiOxNy). Owing to the synergy of TiN coating and Ti doping, the specific capacity of the modified LFP particles increased to ∼159 mAh/g, compared to ∼150 mAh/g of the uncoated one. The modified LFP exhibited a superior cyclic stability with a capacity retention of ∼89% after 1,000 cycles of charge-discharge at a 2C rate at room temperature, whereas the failure of uncoated LFP began after only 500 cycles. A significant reduction of impedance was observed on the TiN ALD-modified LFP, and SEM results showed that this modification restricted severe growth of solid permeable interface layer on the surface of cathode