A Synergistic Effect of Na⁺ and Al³⁺ Dual Doping on Electrochemical Performance and Structural Stability of LiNi_0.88Co_0.08Mn_0.04O₂ Cathodes for Li-Ion Batteries

Abstract

The synergistic effect of Na + /Al 3+ dual doping is investigated to improve the structural stability and electrochemical performance of LiNi 0.88 Co 0.08 Mn 0.04 O 2 cathodes for Li-ion batteries. Rietveld refinement and density functional theory calculations confirm that Na + /Al 3+ dual doping changes the lattice parameters of LiNi 0.88 Co 0.08 Mn 0.04 O 2 . The changes in the lattice parameters and degree of cation mixing can be alleviated by maintaining the thickness of the LiO 6 slab because the energy of Al−O bonds is higher than that of transition metal (TM)−O bonds. Moreover, Na is an abundant and inexpensive metal, and unlike Al 3+ , Na + can be doped into the Li slab. The ionic radius of Na + (1.02 Å) is larger than that of Li + (0.76 Å); therefore, when Na + is inserted into Li sites, the Li slab expands, indicating that Na + serves as a pillar ion for the Li diffusion pathway. Upon dual doping of the Li and TM sites of Ni-rich Ni 0.88 Co 0.08 Mn 0.04 O 2 (NCM) with Na + and Al 3+ , respectively, the lattice structure of the obtained NNCMA is more ideal than those of bare NCM and Li + -and Na + -doped NCM (NNCM and NCMA, respectively). This suggests that NNCMA with an ideal lattice structure presents several advantages, namely, excellent structural stability, a low degree of cation mixing, and favorable Li-ion diffusion. Consequently, the rate capability of NNCMA (83.67%, 3 C/0.2 C), which presents favorable Li-ion diffusion because of the expanded Li sites, is higher than those of bare NCM (78.68%), NNCM (81.15%), and NCMA (83.18%). The Rietveld refinement, differential capacity analysis, and galvanostatic intermittent titration technique results indicate that NNCMA exhibits low polarization, favorable Li-ion diffusion, and a low degree of cation mixing; moreover, its phase transition is hindered. Consequently, NNCMA demonstrates a higher capacity retention (84%) than bare NCM (79%), NNCM (82%), and NCMA (82%) after 50 cycles at 1 C. This study provides insight into the fabrication of Ni-rich NCMs with excellent electrochemical performance. KEYWORDS: cathode material, Li-ion battery, LiNi 0.88 Co 0.08 Mn 0.04 O 2 , Na doping, Al doping, dual doping

Dual doping with cations and anions for enhancing the structural stability of the sodium-ion layered cathode

“…† It is also noted that calculating the formation energy for verifying the thermodynamical stability of doped structure has been implemented widely. 40,44,45 For example, a previous study of simultaneous doping Na and Al show that the formation of dual-doped structure has been suggested by comparing the formation energy and further confirmed by the experiments. 44 Of course, constructing the phase diagram by computing all relevant phases will be more comprehensive in confirming the thermodynamical stability.…”

“…40,44,45 For example, a previous study of simultaneous doping Na and Al show that the formation of dual-doped structure has been suggested by comparing the formation energy and further confirmed by the experiments. 44 Of course, constructing the phase diagram by computing all relevant phases will be more comprehensive in confirming the thermodynamical stability. However, from the perspective of high-throughput computational screening, it is not practical to consider all of the phases and calculate their energy values.…”

Phosphorylation of Li-Rich Mn-Based Layered Oxides for Anion Redox and Structural Stability

“…As displayed in Figure S4a, all the diffraction peaks, except for those in the 2-θ range of 20–30°, can be assigned to the layered α-NaFeO 2 structure, suggesting the R 3̅ m hexagonal phase . The distinct splits of (006)/(102) and (108)/(110) indicate the high crystallinity of the hexagonal structure . The weak peaks, enlarged in Figure S4b, are related to the superstructure of the Li 2 MnO 3 -like component ( C 2/ m space group), in accordance with the PDF card (PDF no 84-1634).…”

“…25 The distinct splits of (006)/(102) and (108)/(110) indicate the high crystallinity of the hexagonal structure. 26 The weak peaks, enlarged in Figure S4b, are related to the superstructure of the Li 2 MnO 3 -like component (C2/m space group), 27 in accordance with the PDF card (PDF no 84-1634). Any additional peaks are not observed in all the XRD patterns, meaning that all samples are pure without any obvious impurities.…”

Low-cobalt active cathode materials for high-performance lithium-ion batteries: synthesis and performance enhancement methods

“…Recently, Park et al have doped LiNi 0.88 Co 0.08 Mn 0.04 O 2 with Na + /Al 3+ and evaluated the effect of change in lattice parameters on the cycling performance of the material. 155 Singly doped and dual doped materials are synthesized by sintering bare NCM with LiOH, NaOH, and Al(NO 3 ) 3 ·9H 2 O at 500 °C for 5 h and then at 750 °C for 12 h in an O 2 atmosphere followed by cooling to room temperature. The as-synthesized materials are termed NCMA [Li(Ni 0.88 Co 0.08 Mn 0.04 ) 0.995 Al 0.005 O 2 ], NNCM [Li 0.995 Na 0.005 (Ni 0.88 Co 0.08 Mn 0.04 )–O 2 ] and NNCMA [Li 0.995 Na 0.005 (Ni 0.88 Co 0.08 Mn 0.04 ) 0.995 Al 0.005 O 2 ].…”