Role of Na⁺in the Cation Disorder of [Li_1-xNa_x]NiO₂as a Cathode for Lithium-Ion Batteries

Abstract

LiNiO 2 is a promising cathode material for lithium ion batteries because of its high specific capacity (approximately 220 mA h g −1 ). However, there are several challenging issues in the development of LiNiO 2 , including its poor cycle and rate performance because of its structural deterioration due to thermodynamically unstable Ni 3+ . This paper demonstrates the role of Na + in the electrochemical performance and structural stability of [Li 1-x Na x ]NiO 2 (x = 0, 0.005, 0.01, 0.025, and 0.05). Charge disproportionation Ni 3+ → Ni 2+ and Ni 4+ in LiNiO 2 increases the cation mixing of Li + and Ni 2+ during cycling, resulting in the poor cycle performance of LiNiO 2 . However, Na + in [Li 1-x Na x ]NiO 2 mitigates the charge disproportionation because of the larger size of Na + than Li + , leading to the improved structural stability of [Li 1-x Na x ]NiO 2 . Consequently, Na + -doped LiNiO 2 alleviates the increase in the cation mixing of Li + and Ni 2+ during cycling compared to bare LiNiO 2 . This results in the improved cycle performance of [Li 1-x Na x ]NiO 2 (x = 0.05), such as approximately 76% of capacity retention after 100 cycles. Moreover, the substitution of Li + with Na + in LiNiO 2 improves the storage characteristics of [Li 1-x Na x ]NiO 2 , leading to a negligible capacity loss even after long-term storage.

Surface and Interfacial Chemistry in the Nickel‐Rich Cathode Materials

“…Recently, Kim et al. enhanced the structural/interfacial stability of the LiNiO 2 cathode by doping the Na + ions in the lithium site . They demonstrated that the Na + ions in the cathode structure suppressed the charge disproportionation reactions of the trivalent nickel ions (2Ni 3+ →Ni 2+ +Ni 4+ ), which decreased the Li/Ni disordering.…”

“…Moreover, the introduction of the electrochemically inactive dopants into the bulk lithium site could also contribute to the stable interfacial characteristics in the nickel-rich cathode materials. The Na [35,37] and Mg [32][33] were representative dopants for the substitution of lithium site because the ionic radius of the Na + and Mg 2 + ions was similar with the lithium ions. The incorporation of the Mg 2 + ions into the lithium site reinforced the interatomic bonding strength between transition metal layer and oxygen layer, preventing drastic lattice shrinkage during lithium de-intercalation.…”

“…[148] Recently, Kim et al enhanced the structural/ interfacial stability of the LiNiO 2 cathode by doping the Na + ions in the lithium site. [37] They demonstrated that the Na + ions in the cathode structure suppressed the charge disproportionation reactions of the trivalent nickel ions (2Ni 3 + !Ni 2 + + Ni 4 + ), which decreased the Li/Ni disordering. In addition, the Na + ions that were served as the pillar layer in the lithium site could guarantee the stable interfacial structure because of the restrained spontaneous reduction of the tetravalent nickel ions at fully charge state.…”

“…To mitigate the cathode reactivity with the electrolyte, there are five approaches for the development of high energy LIBs: (1) the incorporation of electrochemically inactive elements into the cathode structure, [30][31][32][33][34][35][36][37] (2) the introduction of the concentration gradient, (3) the introduction of surface coating layer on the cathode, [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56] (4) the morphological changes to the porous structure, and (5) the crystallinity tuning from the polycrystalline to the single crystalline cathode. [57][58][59][60][61][62][63][64][65][66] With respect to the first approach, it could improve the interfacial stability by inhibiting the transition metal reductions.…”

Coprecipitation and Characterization of Na Substituted LiMn0.5Ni0.5O2 for Lithium ion Battery Cathodes

“…Một số nhóm khác lại cho thấy chỉ có hằng số mạng c tăng lên trong khi hằng số mạng a giảm đi khi thay thế Na cho Li [7,8]. Các kết quả tính toán trong báo cáo này phù hợp với một số công bố khác khi cho thấy cho thấy hằng số mạng c tăng mạnh hơn so với hằng số mạng a khi nồng độ Na thay thế tăng lên [16][17][18]. Ảnh SEM của các mẫu LiMn0.5Ni0.5O2 và Li0.8Na0.2Mn0.5Ni0.5O2 được thể hiện tương ứng trên các hình 4a và 4b.…”