Ni-rich Li[Ni x Co y Mn 1−x−y ]O 2 cathodes (x = 0.6, 0.8, 0.9, and 0.95) were tested to characterize the capacity fading mechanism of extremely rich Ni compositions. Increasing the Ni fraction in the cathode delivered a higher discharge capacity (192.9 mA h g −1 for Li[Ni 0.6 Co 0.2 Mn 0.2 ]O 2 versus 235.0 mA h g −1 for Li[Ni 0.95 Co 0.025 Mn 0.025 ]O 2 ); however, the cycling stability was substantially reduced. Li[Ni 0.6 Co 0.2 Mn 0.2 ]O 2 and Li[Ni 0.8 Co 0.1 Mn 0.1 ]O 2 retained more than 95% of their respective initial capacities after 100 cycles, while the capacity retention of Li[Ni 0.9 Co 0.05 Mn 0.05 ]O 2 and Li[Ni 0.95 Co 0.025 Mn 0.025 ]O 2 was limited to 85% during the same cycling period. The relatively inferior cycling stability of Li[Ni x Co y Mn 1−x−y ]O 2 with x > 0.8 is attributed to the phase transition near the charge-end, causing an abrupt anisotropic shrinkage (or expansion during discharge), which was suppressed for compositions of x < 0.8. Residual stress stemming from the phase transition destabilized the internal microcracks and allowed the microcracks to propagate to the surface, providing channels for electrolyte penetration and subsequent degradation of the exposed internal surfaces formed by the microcracks. Further developments in particle morphology are required to dissipate the intrinsic lattice strain, stabilize the surface, and modify the composition to attain a satisfactory long-term cycling stability, and hence battery life.

Future generations of electric vehicles require driving ranges of at least 300 miles to successfully penetrate the mass consumer market. A significant improvement in the energy density of lithium batteries is mandatory while also maintaining similar or improved rate capability, lifetime, cost, and safety. The vast majority of electric vehicles that will appear on the market in the next 10 years will employ nickel-rich cathode materials, LiNi1–x–y Co x Al y O2 and LiNi1–x–y Co x Mn y O2 (x + y < 0.2), in particular. Here, the potential and limitations of these cathode materials are critically compared with reference to realistic target values from the automotive industry. Moreover, we show how future automotive targets can be achieved through fine control of the structural and microstructural properties.

Boron‐doped Li[Ni0.90Co0.05Mn0.05]O2 cathodes are synthesized by adding B2O3 during the lithiation of the hydroxide precursor. Density functional theory confirms that boron doping at a level as low as 1 mol% alters the surface energies to produce a highly textured microstructure that can partially relieve the intrinsic internal strain generated during the deep charging of Li[Ni0.90Co0.05Mn0.05]O2. The 1 mol% B‐Li[Ni0.90Co0.05Mn0.05]O2 cathode thus delivers a discharge capacity of 237 mAh g−1 at 4.3 V, with an outstanding capacity retention of 91% after 100 cycles at 55 °C, which is 15% higher than that of the undoped Li[Ni0.90Co0.05Mn0.05]O2 cathode. This proposed synthesis strategy demonstrates that an optimal microstructure exists for extending the cycle life of Ni‐rich Li[Ni1‐x‐yCoxMny]O2 cathodes that have an inadequate cycling stability in electric vehicle applications and indicates that an optimal microstructure can be achieved through surface energy modification.

Ni-rich Li­[Ni1–x–y Co x Al y ]­O2 (NCA) cathodes (1 – x – y = 0.8, 0.88, and 0.95) are synthesized to investigate the capacity fading mechanism of Ni-rich NCA cathodes. The capacity retention and thermal property of the cathodes deteriorate as their discharge capacity increases when the Ni fraction is increased. The capacity fading correlates well with the anisotropic volume variations caused by the H2–H3 phase transition and the resulting extent of microcracking. Although all three cathodes start to develop microcracks after being charged to 3.9 V, the potential at which microcracks propagated to the outer surface of the particle decreases with increasing Ni content. These microcracks undermine the mechanical integrity of the cathode and facilitate electrolyte penetration into the particle core, which accelerates surface degradation of the internal primary particles. Therefore, mitigating or delaying the H2–H3 phase transition is key to improving the cycling performance of Ni-rich NCA cathodes.

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.

It is commonly believed that the formation of a solid−electrolyte interphase (SEI) is the main reason for improved electrode performance in rechargeable batteries. However, herein we present a new interfacial model that may change the thinking about the role of SEI, which has prevailed over the past 2 decades. We show that the varied desolvation behavior of mobile ions, which depends on the solvation structure determined by multiple factors (e.g., cations, solvent, anions, and additives) is a critical factor for electrode stability besides the SEI. This interfacial model can predict the intercalating species in graphite electrodes (i.e., Li + (de)intercalation or Li + −solvent co-insertion) in different types of electrolytes (e.g., carbonate-, ether-based electrolyte). The generality of our model is further demonstrated by its ability to interpret the variable lithium plating/stripping in different electrolytes. Our model can predict electrode performance through the proposed cation−solvent interactions and desolvation behaviors and then help develop new types of electrolytes for mobile (ion) batteries.

Electrochemical properties and structural and thermal stability of Li[Ni 0.65 Co 0.13 Mn 0.22 ]O 2 (FCG65), Li[Ni 0.75 Co 0.08 Mn 0.17 ]O 2 (TSFCG75), and Li[Ni 0.85 Co 0.05 Mn 0.10 ]O 2 (TSFCG85) with concentration gradients of Ni and Mn were evaluated to comprehensively demonstrate the effectiveness of compositional gradation for a wide range of Ni-rich Li[Ni x Co y Mn 1−x−y ]O 2 (NCM) cathodes. The discharge capacities of FCG65, TSFCG75, and TSFCG85 were 194.2, 206.8, and 222.2 mAh g −1 , respectively with capacity retention of over 90% after 100 cycles. The high capacities and enhanced cycling stability relative to those of conventional Ni-rich NCM cathodes were attributed to the compositional partitioning, strong crystallographic texture, and unique particle morphology. In addition, the highly correlated particle orientation helped to reduce the anisotropic internal strain induced by Li removal/ extraction from the Ni-rich NCM cathodes. The accelerated aging test (storing the delithiated cathodes in an electrolyte at elevated temperature) reconfirmed the superior stability of the TSFCG85 cathode compared to the commercial Li[Ni 0.82 Co 0.14 Al 0.04 ]O 2 cathode, which exhibited fast structural degradation. Thus, NCM cathodes with concentration gradients represent a viable solution that simultaneously addresses the specific energy density, cycling and chemical stability, and safety issues of Ni-enriched NCM cathodes for general electromobility.

The electrochemical behavior of Na-ion and Li-ion full cells was investigated, using hard carbon as the anode material, and NaNi0.5Mn0.5O2 and LiNi0.5Mn0.5O2 as the cathodes. A detailed description of the structure, phase transition, electrochemical behavior and kinetics of the NaNi0.5Mn0.5O2 cathodes is presented, including interesting comparison with their lithium analogue. The critical effect of the hard carbon anodes pretreatment in the total capacity and stability of full cells is clearly demonstrated. Using impedance spectroscopy in three electrodes cells, we show that the full cell impedance is dominated by the contribution of the cathode side. We discuss possible reasons for capacity fading of these systems, its connection to the cathode structure and relevant surface phenomena.