Synergic titanium nitride coating and titanium doping by atomic layer deposition for stable- and high-performance li-ion battery

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 (TiO_xN_y). 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.