LiF-Dominated SEI Formation via a Lychee-Like PrimaryInterphase for Fast-Charging Natural Graphite Anodes

OPEN ACCESS PAPER Abstract: Natural graphite, with its lower production cost, higher capacity, and superior electrical conductivity than artificial graphite, currently accounts for approximately 40% of the global lithium-ion battery anode market. However, the inadequate compatibility of natural graphite with commercial carbonate ester electrolytes leads to irreversible capacity loss, reduce coulombic efficiency, and rapid capacity decline during cycling. Applying an oxygen-deficient titanium dioxide (TiO2-x) protective layer to natural graphite anodes has been noted as a successful method for improving their structural integrity and cycling stability; however, the fragile solid–electrolyte interphase (SEI) limits their fast-charging capability. In this study, nitrogen atoms are strategically incorporated into the TiO2-x surface structures, creating a lychee-like primary interphase that regulated the interfacial electrochemistry and facilitated the development of a LiF-dominated SEI. The robust LiF-dominated SEI, as examined through ex situ X-ray photoelectron spectroscopy analysis and kinetic evaluations, successfully mitigates interfacial side reactions and enhances bulk charge transfer. Consequently, the modified natural graphite anodes exhibit improved capacities at higher current densities, delivering a stable reversible capacity of 388.9 mAh g−1 after 200 cycles at a rate of 5 C. Dataset: The original TIFF/PNG data from original research. Precisely, there are 5 final, complex Figures below: Figure 1. (a) Schematic of the procedure used for synthesizing TiO2‐x‐yNy@NG. (b) SEM (c) TEM and (d) STEM TiO2‐x‐yNy@NG. EDS maps showing distributions of e) Ti, f) O, and g) N within the area shown in (d) Figure 2. a) XRD patterns, b) Raman spectra, and c) EPR spectra of NG, TiO2‐x@NG, and TiO2‐x‐yNy@NG. XPS spectra of d) Ti 2p, e) O 1s, and f) N 1s core levels in TiO2‐x‐yNy@NG Figure 3. a) Initial charge-discharge curves at 0.1 C. b) Initial CV curves at 0.1 mV s−1. c) Rate performance. d) Comparison of charge-discharge curves at 2 C. e) dQ-dV curve of the TiO2‐x‐yNy@NG anodes. Cycling performance at f) 1 C and g) 5 C in CC‐CV mode the TiO2‐x‐yNy@NG anodes. Cycling performance of full batteries in a voltage range of 2.4‐3.8 V at charge-discharge rate of h) 0.5 C-0.5 C, and i) 0.5 C-1 C Figure 4. CV curves of a) NG, b) TiO2‐x@NG, and c) TiO2‐x‐yNy@NG anodes at different scan rates. d) Li‐ion diffusion coefficient of NG, TiO2‐x@NG, and TiO2‐x‐yNy@NG anodes. e) Nyquist plots of various anodes. f) Associated resistances: electrolyte resistance (Re), SEI resistance (RSEI), and charge transfer resistance (Rct). g) Detailed GITT voltage–time profile. Li‐ion diffusion coefficient during h) lithiation and i) de‐lithiation processes Figure 5. SEM images of a) TiO2‐x‐yNy@NG and b) NG anodes after 500 cycles at 1 C. Ex situ Raman spectra of c) TiO2‐x‐yNy@NG and d) NG anodes before and after 500 cycles at 1 C. XPS F 1s spectra of SEI layers on the surfaces of e) TiO2‐x‐yNy@NG and f) NG anodes after 500 cycles at 1 C. g) Adsorption configurations of FEC molecules on anode surfaces. h) Relative energy distribution of LiF on anode surfaces Funding: This work was supported by the following: European Union’s Horizon Europe Research and Innovation Program under grant agreement No. 101087143 (Electron Beam Emergent Additive Manufacturing (EBEAM)), National Natural Science Foundation of China (Grant No. 52071225), Norway Grants project No. 2019/34/H/ST8/00547 funded by the National Science Center, National Key R&D Program of China (2021YFB3800300), National Natural Science Foundation of China (Grant Nos. 22179143 and 22002176).