Suppressed Lattice Oxygen Release via Ni/Mn Doping from Spent LiNi_0.5Mn_0.3Co_0.2O₂ toward High-Energy Layered-Oxide Cathodes

Abstract

LiCoO2 has suffered from poor stability under high voltage as a result of insufficient Co–O bonding that causes lattice oxygen release and lattice distortions. Herein, we fabricated a high-voltage LiCoO2 at 4.6 V by doping with Ni/Mn atoms, which are obtained from spent LiNi0.5Mn0.3Co0.2O2 cathode materials. The as-prepared high-voltage LiCoO2 with Ni/Mn substitutional dopants in the Co layer enhances Co–O bonding that suppresses oxygen release and harmful phase transformation during delithiation, thus stabilizing the layered structure and leading to a superior electrochemical performance at 4.6 V. The pouch cell of modified LiCoO2 exhibits a capacity retention of 85.1% over 100 cycles at 4.5 V (vs graphite). We found that our strategy is applicable for degraded LiCoO2, and the regenerated LiCoO2 using this strategy exhibits excellent capacity retention (84.1%, 100 cycles) at 4.6 V. Our strategy paves the way for the direct conversion of spent batteries into high-energy-density batteries.

Direct regeneration of degraded lithium-ion battery cathodes with a multifunctional organic lithium salt

“…13) show that the major peaks in charge and discharge are respectively due to the Li-ion de-insertion and insertion reactions. According to the Randles-Sevcik equation [35][36][37] ,…”

Revisiting Cationic Doping Impacts in Ni-Rich Cathodes

“…7−10 Various modification methods have been studied to cope with the issues in pursuing safe operation and practical application. 11,12 Among them, cationic doping of electrochemically inactive species is one feasible strategy to improve the electrochemical performance. 13,14 Monovalent and divalent metal dopants, e.g., Na + and Mg 2+ , are believed prone to occupy the Li site, while trivalent, tetravalent, and higher-valent metal dopants, e.g., Al 3+ , Ti 4+ , and Nb 5+ , are prone to occupy the transition-metal site.…”

“…In recent years, the developing Ni-rich layered oxide cathode material has been a state-of-the-art research direction because the specific capacity of layered rock-salt oxides LiTMO 2 (TM = transition metals) is significantly improved with increasing Ni content. , The widely studied LiNi x Co y Mn z O 2 (NCM, x + y + z = 1) system usually delivers ∼150 mAh g –1 reversible specific discharge capacity with x ≤ 0.5, while the Ni-rich materials, e.g., LiNi 0.8 Co 0.1 Mn 0.1 O 2 and LiNi 0.80 Co 0.15 Al 0.05 O 2 , can deliver ∼200 mAh g –1 specific discharge capacity with the cutoff voltage of 3.0–4.3 V. , However, the enhanced specific capacity with increasing Ni content is at the expense of stability and cyclability . The electrochemical degradation and safety hazards are serious problems of battery failure, both of which are deeply linked with oxygen release in Ni-rich cathodes: the structural deterioration including ordered–disordered structural change and layered–spinel phase transition are associated with lattice oxygen loss; the gaseous oxygen induces severe parasitic reactions with electrolyte at high state of charge. − Various modification methods have been studied to cope with the issues in pursuing safe operation and practical application. , Among them, cationic doping of electrochemically inactive species is one feasible strategy to improve the electrochemical performance. , Monovalent and divalent metal dopants, e.g., Na + and Mg 2+ , are believed prone to occupy the Li site, while trivalent, tetravalent, and higher-valent metal dopants, e.g., Al 3+ , Ti 4+ , and Nb 5+ , are prone to occupy the transition-metal site. − Researchers generally accept the opinion that proper doping strategies by these various dopants have a positive impact on the electrochemical performancemainly in the aspect of cyclability for long-term cycling. Al 3+ , the most prevailing isovalent dopant in the transition-metal site, has been found to stabilize high-valent Ni at high state of charge and increase the migration barrier of transition metals and has achieved great commercial success. − Higher-valent dopants, such as Ti 4+ , Zr 4+ , and Nb 5+ , are reported to provide a stronger bond with oxygen and mitigate cation mixing, thus helping to maintain the structure integrity and improve cycling stability. − Specifically, calculations suggest that oxygen binds more strongly to some dopants than electrochemically active Ni and Co, and cationic doping can increase the oxygen vacancy formation energy by less covalency of metal–oxygen bonding. − Such a stabilization effect on lattice oxygen activity is sometimes considered as an improvement of inherent material property, also one of the critical attributions of electrochemica...…”

“…Al 3+ , the most prevailing isovalent dopant in the transition-metal site, has been found to stabilize high-valent Ni at high state of charge and increase the migration barrier of transition metals and has achieved great commercial success. − Higher-valent dopants, such as Ti 4+ , Zr 4+ , and Nb 5+ , are reported to provide a stronger bond with oxygen and mitigate cation mixing, thus helping to maintain the structure integrity and improve cycling stability. − Specifically, calculations suggest that oxygen binds more strongly to some dopants than electrochemically active Ni and Co, and cationic doping can increase the oxygen vacancy formation energy by less covalency of metal–oxygen bonding. − Such a stabilization effect on lattice oxygen activity is sometimes considered as an improvement of inherent material property, also one of the critical attributions of electrochemical enhancement through the doping strategy. Although a close relation between electrochemical stability and lattice oxygen stability in Ni-rich cathodes has been suggested, ,, direct evidence for that hypothesis has not been given so far, and there still remains an open question: what is true impact of isovalent/high-valent cation doping? Despite vast amounts of research on doping strategies in Ni-based layered cathodes, the cognitive gap is waiting to be filled based on reasonable experimental proofs owing to the lack of quantitative assessment of thermodynamic properties of cathode active materials like lattice oxygen stability from a thermodynamics perspective.…”

“…27−29 Such a stabilization effect on lattice oxygen activity is sometimes considered as an improvement of inherent material property, also one of the critical attributions of electrochemical enhancement through the doping strategy. Although a close relation between electrochemical stability and lattice oxygen stability in Ni-rich cathodes has been suggested, 11,13,30 direct evidence for that hypothesis has not been given so far, and there still remains an open question: what is true impact of isovalent/high-valent cation doping? Despite vast amounts of research on doping strategies in Nibased layered cathodes, the cognitive gap is waiting to be filled based on reasonable experimental proofs owing to the lack of quantitative assessment of thermodynamic properties of cathode active materials like lattice oxygen stability from a thermodynamics perspective.…”