Degradation Mechanism of Ni-Enriched NCA Cathode for Lithium Batteries: Are Microcracks Really Critical?

Abstract

A series of Ni-enriched Li­[Ni x Co y Al z ]­O2 cathodes (x = 0.80–0.95) were synthesized and evaluated comprehensively to investigate the capacity fading mechanism. Capacity retention was shown to be strongly related to the extent of microcracking within the secondary particles. Moreover, the range and limit of the depth of discharge (DOD), which determined the extent of microcracking, critically affected the cycling stability such that the extremely Ni-rich Li­[Ni0.95Co0.04Al0.01]­O2 cathode cycled at an upper DOD of 60% exhibited the poorest capacity retention. The anisotropic strain produced by the H2–H3 phase transition was not fully relieved, and persistent microcracks in the discharged state (3.76 V) allowed the electrolyte to penetrate the particle interior. Resultant extended exposure of the interior primary particles within secondary particle to electrolyte attack accelerated structural damage and eventually undermined the mechanical integrity of the cathode particles.

Enhanced High‐Temperature Electrochemical Performance of Layered Nickel‐Rich Cathodes for Lithium‐Ion Batteries after LiF Surface Modification

“…All observable diffraction peaks can be attributed to the layered hexagonal structure of α‐NaFeO 2 , belonging to the space group Rm. The splitting of the different (006)/(012) and (018)/(110) peaks suggests that these oxides have a well‐developed layered structure . The XRD pattern of the modified material did not change significantly because the coating amount of LiF was small, the coating layer was thin, and LiF existed in an amorphous state.…”

“…The splitting of the different (006)/(012) and (018)/(110) peaks suggests that these oxides have a well-developed layered structure. [22,46,47] The XRD pattern of the modified material did not change significantly because the coating amount of LiF was small, the coating layer was thin, and LiF existed in an amorphous state. The above analysis demonstrates that the coating material does not enter the crystal lattice, and only the coating layer is formed on the surface, which TEM tests further confirmed.…”

“…[14,[18][19][20] HF produced by lithium hydroxide corrodes the electrode material, resulting in an irreversible phase change of the cathode. [21][22][23] Moreover, the dissolution of metal ions is accelerated at high temperatures, causing the layered structure to collapse and the material's thermal stability to deteriorate. [24][25][26][27] To overcome these limitations, surface modification is one of most commonly employed routes, which can suppress side reactions at the electrode/electrolyte interface, thereby improving cycle stability.…”

Surface/Interface Structure Degradation of Ni‐Rich Layered Oxide Cathodes toward Lithium‐Ion Batteries: Fundamental Mechanisms and Remedying Strategies

“…The results reveal that the high cutoff voltage charging induces significant oxidation state inhomogeneities in the cycled particles, eventually bringing about the formation of microcracks in the cycled particles. The extent of microcracks and underlying formation origins with the Ni content above 80 mol% are also recently studied . Typically, the microstructural degradation during the accelerated calendar aging of the Ni‐rich LiNi x Co y Mn 1− x − y O 2 ( x = 0.8 and 0.9) cathodes is characterized, revealing that the microcracks develop and remain across the entire secondary particles even in the fully discharged state and further widen along the grain boundaries because of the electrolyte penetration .…”

Review of Modified Nickel-Cobalt Lithium Aluminate Cathode Materials for Lithium-Ion Batteries

“…Among the series of materials with different ratios of Ni, Co, and Al elements, LiNi 0.8 Co 0.15 Al 0.05 O 2 is the most widely researched material and has attracted full attention and commercialization due to its low cost, nontoxicity, and high-energy density [24]. Tesla is the first company to employ NCA cathode materials to power cars, and it has achieved remarkable success in the electric vehicle industry [25].…”