Probing and Resolving the Heterogeneous Degradation of Nickel‐Rich Layered Oxide Cathodes across Multi‐Length Scales

Abstract

though new energy storage devices such as lithium-sulfur batteries [2] and lithium-air batteries [3] have shown great promise due to large theoretical capacity, lithium ion batteries (LIBs) are still dominating in portable electronic devices, prevailing in electric vehicles, and gradually entering grid-energy storage markets. [4] The unsatisfactory energy density of cathodes is widely recognized as the critical bottleneck for higher-performance LIBs. [5] Among various cathodes, Ni-rich layered lithium transition-metal oxides possessing a larger reversible capacity (>180 mAh g −1) than LiCoO 2 (140 mAh g −1), LiNi 1/3 Co 1/3 Mn 1/3 O 2 (160 mAh g −1), LiMn 2 O 4 (120 mAh g −1), and LiFePO 4 (160 mAh g −1), are regarded as one of the most promising cathodes for the next-generation LIBs. [6] In 2016, American electric vehicle company Tesla launched Model 3 with LiNi 0.85 Co 0.10 Al 0.05 O 2 as the cathode for its electric vehicle battery, a testament to the huge potential of Ni-rich layered oxides (NRLOs) (Scheme 1). NRLO cathodes generally consist of two main categories-LiNi 1−x−y Co x Mn y O 2 (NMC) and LiNi 1−x−y Co x Al y O 2 (NCA). The evolution from LiCoO 2 /LiNiO 2 / LiMnO 2 to LiNi 1−x−y Co x Mn y O 2 has been introduced in previous reviews. [7] Briefly, synthesizing LiCoO 2 with the low-defect density was relatively accessible due to the large difference in ionic radius between Li + and Co 3+ , but the irreversible structural change takes place when more than half a fraction of Li + is extracted from its lattice, restricting the capacity. Stoichiometric LiNiO 2 is difficult to prepare due to the instability of trivalent Ni at high temperatures, and the cation mixing between Li and Ni weakens the cycling stability of LiNiO 2. [8] Synthesis of the layered LiMnO 2 phase is not straightforward either, and the capacity fades rapidly because the structural transformation from layered to spinel phase is inevitable upon cycling. [9] LiNi 1−x−y Co x Mn y O 2 combines the strengths of nickel (high capacity), cobalt (good rate capability), and manganese (benign stability). [7] The redox couples of Ni 2+ /Ni 3+ /Ni 4+ and Co 3+ /Co 4+ contribute to the majority of the capacity. The existence of cobalt suppresses the cation mixing during the synthesis of stoichiometric compounds, while manganese helps stabilize the Ni-rich layered oxides (NRLO) are widely considered among the most promising cathode materials for high energy-density lithium ion batteries. However, the high proportion of Ni content accelerates the cycling degradation that restricts their large-scale applications. The origins of degradation are indeed heterogeneous and thus there are tremendous efforts devoted to understanding the underlying mechanisms at multi-length scales spanning atom/lattice, particle, porous electrode, solid-electrolyte interface, and cell levels and mitigating the degradation of the NRLO. This review combines various advanced in situ/ex situ analysis techniques developed for resolving NRLO degradation at multi-length scales and aims...

A nonflammable electrolyte for ultrahigh-voltage (4.8 V-class) Li||NCM811 cells with a wide temperature range of 100 °C

“…5f, Ni K-edge profile of NCM811 at fully charged state (4.7 V), as a reflection of oxidation states of transition metal ions, in HV electrolyte shifts to higher energy than that in base electrolyte, but almost overlaps with that of NCM811 without cycling, indicating the higher oxidation state of Ni in HV electrolyte. The lower oxidation state of Ni in base electrolyte is ascribed to the constant side reaction between electrolytes and dissolved metal ions, thick CEI with high impedance, rock-salt phase, and/or micro-cracking in the cathode particle, which prevent charging Ni to higher oxidation state; 45,46 while the higher oxidation state of Ni in HV electrolyte is associated with the structural stability of both CEI and bulk cathode induced by HV electrolyte, in consistent with previous results. The minimal changes of the XRD peaks of cycled NCM811 (Fig.…”

Effect of Magnesium Doping on Voltage Decay of Nickel‐Rich Cathode Materials

“…[47][48][49] Raman spectrometer is a powerful technique that can examine the near-surface region of the transition metal-oxygen (TMÀ O) bond by evaluating the frequency shift of the scattered beam relative to the incident laser beam. [71] Raman shift is evaluated by the vibrational energy of the interatomic bonds of the lattice, which is affected by the oxidation state, lattice symmetry, and strains. [72] Figure 2 shows the Raman spectra of the samples Mg0-Mg2.…”

Synchrotron X‐Ray Tomography for Rechargeable Battery Research: Fundamentals, Setups and Applications

“…This is accomplished by the energy tunability of synchrotron X‐ray beams which enables the study of energy dependence of the characteristic absorption coefficient of each voxel point in 3D space. [ 102,103 ] Yu et al. [ 104 ] used TXM‐XANES technique to characterize the nanoscale battery reactions within a battery built with LiFePO 4 particles.…”