Tuning the Li/Ni Disorder of the NMC811 Cathode by Thermally Driven Competition between Lattice Ordering and Structure Decomposition

Abstract

Ni-rich layered LiNi x Mn y Co z O2 (NMC) cathodes for lithium-ion batteries are receiving a lot of attention owing to their promising large capacity, whereas the high content of Ni results in several issues including poor thermal stability and serious Li/Ni disorder. Although a little degree of the Li/Ni disorder may be beneficial for the structural stability of NMC cathodes and even migration of Li ions, a high degree of the Li/Ni disorder certainly deteriorates their electrochemical performances. Therefore, tuning the Li/Ni disorder is of great interest in the development of safer NMC cathodes with larger accessible capacity. Post-synthesis annealing is a facile and low-cost way to manipulate lattice defects, yet has not been utilized to optimize the Ni-rich NMC cathodes. In this work, we report that post-synthesis annealing can induce the competition between lattice ordering and structure decomposition. The thermal annealing promoted that lattice ordering would prevail until the decomposition of oxygen lattice. Once the annealing temperature reaches the critical temperature to form oxygen vacancies, Ni ions can easily migrate into the Li slab. The Li/Ni disorder can be facilely tuned through post-synthesis annealing to optimize the electrochemical performances of NMC cathodes.

A perspective on sustainable energy materials for lithium batteries

“…The high Ni and low Co can lead to a high capacity and low price, meanwhile a poor cycling stability and high safety hazard. Electrolyte modification, 31–33 interfacial design, 34–36 postsynthesis annealing, 37 and morphology regulation, 38 can efficiently relieve these issues. LFP: Reported firstly in 1997 by Goodenough et al., LFP has become an important electrode material (Figure 3B), 39 which has excellent long‐term cycling ability, thermal stability, environmental friendliness, and low cost. Compared with LCO and NMC, the theoretical capacity of LFP is relatively low (170 mAh/g at room temperature), which limits the practical application of LFP, especially in EVs 40 .…”

“…The high Ni and low Co can lead to a high capacity and low price, meanwhile a poor cycling stability and high safety hazard. Electrolyte modification, [31][32][33] interfacial design, [34][35][36] postsynthesis annealing, 37 and morphology regulation, 38 can efficiently relieve these issues. 3B), 39 which has excellent long-term cycling ability, thermal stability, environmental friendliness, and low cost.…”

Synthesis and Manipulation of Single-Crystalline Lithium Nickel Manganese Cobalt Oxide Cathodes: A Review of Growth Mechanism

“…Lithium nickel manganese cobalt oxide (NMC) cathodes have been critical pillars of advanced lithium ion batteries at current state (Chen et al, 2019;Xu et al, 2019;Zhou et al, 2019;Kim et al, 2020;Li et al, 2020;Wang et al, 2020b;Wu et al, 2020;Zhang, 2020;Zheng et al, 2020). The particle's crystallinity and morphology can put significant influences on the energy density, cycling stability, and rate capability of the NMC cathodes in practical applications (Liu et al, 2018;Fan et al, 2020).…”

“…The polycrystalline nature of the secondary particles presents many issues, including (1) low tap density (<3.3 g cm −3 ) compared with the single-crystalline LiCoO 2 cathode (3.9 g cm −3 ), which leads to an inadequate volumetric energy density (Kim et al, 2018 ), (2) the formation of microcracks inside the secondary particle incurred by the anisotropic lattice expansion and shrink during charging/discharging, which gradually deteriorates the cycling stability (Kim et al, 2018 ; Liu et al, 2018 ), and (3) the porous structure of the secondary particle prevents homogeneous carbon coating on each primary particle, which results in unsatisfactory electrical contact between the active material and the current collector (Kimijima et al, 2016b ). In the recent decade, the chasing of larger gravimetric capacity has pushed the nickel content of the NMC to over 60%; as a tradeoff larger gravimetric capacity, these nickel-rich NMC cathodes are suffering more serious issues caused by the polycrystalline secondary particles (Dixit et al, 2017 ; Kim et al, 2018 ; Lee et al, 2018 ; Liang et al, 2018 ; Ryu et al, 2018 ; Fan et al, 2020 ; Wang et al, 2020b ). The mandatory increase of the tap density to over 3.3 g cm −3 generally leads to rapid capacity fading since the polycrystalline secondary particles would crack and collapse during high-pressure electrode pressing (Kim et al, 2018 ).…”

Gas impurity in calcination atmosphere governing electrochemical properties of LiNi0.8Mn0.1Co0.1O2 cathode material for lithium ion batteries

“…Representative approaches include lattice doping, [14,15,16] surface processing/modification and tuning of material compositions. [17,18,19,20] Other synthetic conditions, such as calcination temperature, [22,23] calcination atmosphere [20] or are important in determining structural properties (incl. Li/Ni cation mixing) and thus influencing the electrochemical performance of high Ni cathode.…”