One-Step Synergy of Coating and Doping By TiN Atomic Layer Deposition for Significant Improvement on Li-Ion Battery

Abstract

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, synergic coating and doping on LiFePO4 (LFP) was carried out by titanium nitride (TiN) ALD. The composition of TiN layer on the surface of LFP particles was interpreted as a combination of TiN and titanium oxynitride (TiOxNy) by X-ray photoelectron spectroscopy (XPS). The Ti-doped phase was formed by reactions between TiCl4 precursor and LFP during ALD, and this phase was consistent with lithium titanium phosphate. Owing to the synergy of TiN coating and Ti doping, the specific capacity of modified LFP increased to ~159 mAh/g, which was ~93% of its theoretical capacity; after 1,000 cycles of charge-discharge at a 2C rate at room temperature, the modified LFP exhibited a super stable cyclic behavior with a capacity retention of ~89%, whereas the failure of uncoated LFP began after only 500 cycles. The electrochemical impedance spectra showed TiN ALD-modified LFP significantly lowered the film and charge-transfer resistances, and a restricted growth of solid permeable interface layer on the surface of cathode was confirmed by SEM.