Degradation Mechanism of Highly Ni-Rich Li[Ni_xCo_yMn_1–x–y]O₂ Cathodes with x > 0.9

Abstract

A series of Ni-rich Li[Ni x Co (1−x)/2 Mn (1−x)/2 ]O 2 (x = 0.9, 0.92, 0.94, 0.96, 0.98, and 1.0) (NCM) cathodes are prepared to study their capacity fading behaviors. The intrinsic trade-off between the capacity gain and compromised cycling stability is observed for layered cathodes with x ≥ 0.9. The initial specific capacities of LiNiO 2 and Li[Ni 0.9 Co 0.05 Mn 0.05 ]O 2 are 245 mAh g −1 (91% of the theoretical capacity) and 230 mAh g −1 , and their corresponding capacity retentions are 72.5% and 88.4%. However, the capacity retention characteristic deteriorates at an increasingly faster rate for x > 0.95, in contrast with the nearly linear increase of specific capacity. The fast capacity fading stems from the chemical attack of the cathode by the electrolyte infiltrated through the microcracks, resulting from the mechanical instability inflicted by the anisotropic internal strain caused by the H2 ⇆ H3 phase transition. Thus, the capacity fading of the NCM cathodes for x > 0.9 critically depends on the extent of the H2 → H3 phase transition. Retardation or protraction of the H2 ⇆ H3 phase transition by engineering the microstructure should improve the cycle life of these highly Ni-enriched NCM cathodes. KEYWORDS: Ni-rich layered Li[Ni x Co y Mn 1−x−y ]O 2 cathode, capacity fading mechanism, microcracks, high-energy density, lithium-ion batteries

Realizing Superior Cycle Stability of a Ni‐Rich Layered LiNi0.83Co0.12Mn0.05O2 Cathode with a B2O3 Surface Modification

“…Studies confirmed that the H2!H3 phase transition can cause rapid volume expansion in the c-direction and is irreversible, being one of the most important factors for the decline of discharge capacity. [10] The intensity of the H2! H3 phase transition peak for the bare sample drops significantly and shifts to the right after 100 cycles (Figure 8a), revealing the poor reversibility of the H2!H3 phase transition during cycling.…”

“…Nevertheless, a high Ni content causes severe Li + /Ni 2+ cation mixing, phase transitions, microcracks and side reactions, which accelerate the performance degradation of the cathode material. Of the above problems, interfacial problems are urgent issues to be solved.…”

Stabilizing Ni‐Rich LiNi0.92Co0.06Al0.02O2 Cathodes by Boracic Polyanion and Tungsten Cation Co‐Doping for High‐Energy Lithium‐Ion Batteries

“…According to reports in the literature, the dramatical decrement of the intensity of redox peaks in the dQ dV À 1 profile during cycling is likely caused by the structural degradation of the cathode arising from the H2-H3 phase transition. [30,31] The huge decaying redox peaks during cycling are observed in the dQ dV À 1 profile of NCA92, while the redox peaks for NCA92-W-B sample hardly changes during cycling, suggesting that the structure is relatively stable during cycling. Therefore, it could be inferred that W 6 + and BO 3 3À co-doping could suppress the detrimental H2-H3 phase transition.…”

Enhancing surface oxygen retention through theory-guided doping selection in Li1−xNiO2 for next-generation lithium-ion batteries

“…However, widespread application of Ni-rich cathode materials is limited by their insufficient capacity retention and thermal stability. 6,7 Li 1Àx NiO 2 undergoes several reversible phase transitions during Li + intercalation and deintercalation, [8][9][10] whereof one, at high state-of-charge (V > 4.1 V), leads to a signicant shrinkage of the material in the c-axis direction 11 and hence incurs extensive structural damage from the repeated lattice contraction and expansion. 12 The developed cracks expose fresh cathode surface area to the electrolyte, thus accelerating detrimental, parasitic reactions.…”