Restraining the Octahedron Collapse in Lithium and Manganese Rich NCM Cathode toward Suppressing Structure Transformation

Abstract

Compared with the advanced anode, the energy density of LIBs is more largely determined by discharge capacity and voltage of the cathode. [3][4][5] Lithium and manganese rich nickel cobalt manganese oxide (LMRNCM), xLi 2 MnO 3 •(1-x)LiTMO 2 (TM (transition metal) = Mn, Ni, Co), has been considered as an attractive next-generation cathode candidate owing to its high energy density (≈1000 Wh kg −1 ) and low cost. [6] According to the charge compensation mechanism and the energy level theory, when the Li + extraction voltage is lower than 4.4 V, the TM ions of high electron energy level is mainly oxidized to maintain electrical neutrality. [7,8] When the voltage is higher than 4.4 V, the electronic energy level of TM 4+ →TM n+ (n > 4) is lower than that of O 2− →O m− (0 ≤ m < 2), [9,10] and the electrical neutrality is maintained by the oxidation of lattice oxygen. On the one hand, lattice oxygen redox reaction provides higher specific capacity, [11,12] which is a key factor that determines high energy density. On the other hand, the unstable high-valence lattice oxygen accelerates the degradation of the LMRNCM layered structure. [13] Specifically, high-valence oxygen is unstable in the crystal lattice, and is easily released with Li + in the form of Li 2 O. [14] The absence of lattice oxygen in the octahedron causes unstable Lithium and manganese rich nickel cobalt manganese oxide (LMRNCM), as an attractive high energy density cathode for advanced lithium-ion batteries (LIBs), suffers from inevitable lattice oxygen release, irreversible transition metal (TM) ion migration, and interface side reactions at high charge cut-off voltage. Herein, a facile and efficient surface strategy is proposed to stabilize the layered structure by regulating the chemical bond interaction between the polyacrylonitrile (PAN) binder and the LMRNCM particles. Due to the high retention of discharge specific capacity and average discharge voltage, the energy density retention of the PAN-modified LMRNCM sample is up to 80.12% after 300 cycles at 100 mA g −1 current density, and the initial Coulombic efficiency and rate capacity are also improved simultaneously. Experimental and density functional theory evidence demonstrates that the exceptional performance is caused by the coordination bond interaction between the carbon-nitrogen-triple-bond of PAN and the TM ion in the unstable transition metal oxygen octahedron. The interaction suppresses the irreversible migration of TM ions by increasing the energy barrier, and ensures that the PAN adheres to the LMRNCM particles tightly, which relieves electrolyte corrosion and enhances cohesiveness. This work exploits a modification strategy to stabilize the LMRNCM-layered structure for high-energy density LIB applications.

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

“…105,106 Cation doping and interface engineering are two of the efficient strategies to prevent the lattice oxygen escape. 100,107,108…”

“…It is observed that at a highly delithiated stage (voltage > 4.4 V), O 2− oxidation is more favored compared to transition metal oxidation. 99,100 At this stage, the highly reactive Ni 4+ of the Ni-rich NCM moiety reduces to Ni 2+ by oxidizing the electrolyte. In order to maintain the charge neutrality, the lattice O 2− oxidizes and escapes from the NCM lattice.…”

“…105,106 Cation doping and interface engineering are two of the efficient strategies to prevent the lattice oxygen escape. 100,107,108 5 Strategies to improve the electrochemical performance High Ni-content NCMs, specically NCM-811, would be a potential cathode material for the production of commercial high energy Li-ion batteries only if the issues can be addressed rationally. Several efforts and scientic advancements are in progress worldwide to improve the LIB performance in terms of specic capacity, energy density, rate capability and cycling stability.…”

Engineering commercial polycrystalline precursors to single crystal Ni-rich cathodes with outstanding long-cycle performance

“…30,31 These unique properties have aroused tremendous research interest in the mechanism investigation and development of Ni-rich cathodes which are highly sensitive to morphology and size distribution. 32,33 Ryu et al 34 found that a traditional single-crystal NCM cathode shows only 91.1% capacity retention aer 100 cycles due to the stress generated by multi-phase coexistence and the uneven Li + concentration inside the single-crystal NCM cathode. Xiao et al 35 observed a reversible planar gliding and microcracking in single crystal NCM in which the stability is governed by reduced crystal size smaller than 3.5 mm and the depth of charge.…”

Prospective Application, Mechanism, and Deficiency of Lithium Bis(oxalate)Borate as the Electrolyte Additive for Lithium‐Batteries

“…[ 4,5 ] For example, the nickel (Ni) in NCM materials is easy to dissolute into electrolyte and deposit on the graphite cathode, while cobalt content will be reduced, resulting in an unstable architecture of the NCM materials, which can easily react with electrolyte to reduce the capacity of LIBs. [ 6,7 ] Therefore, the electrolyte always needs additives to form a dense and homogeneous film that can isolate the electrolyte from the cathode material and prevent the influence of side reactions. [ 8,9 ] Lithium bis(oxalate)borate (LiBOB) is such a classic additive, used to improve the multiplicity and cycling performance of LIBs.…”