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

Microstructures of layered Ni-rich cathodes for lithium-ion batteries

Millions of electric vehicles (EVs) on the road are powered by lithium-ion batteries (LIBs) based on nickel-rich layered oxide (NRLO) cathodes, and they suffer from a limited driving range and safety concerns. Increasing the Ni content is a key way to boost the energy densities of LIBs and alleviate the EV range anxiety, which are, however, compromised by the rapid performance fading. One unique challenge lies in the worsening of the microstructural stability with a rising Ni-content in the cathode. In this review, we focus on the latest advances in the understanding of NLRO microstructures, particularly the microstructural degradation mechanisms, state-of-the-art stabilization strategies, and advanced characterization methods. We first elaborate on the fundamental mechanisms underlying the microstructural failures of NRLOs, including anisotropic lattice evolution, microcracking, and surface degradation, as a result of which other degradation processes, such as electrolyte decomposition and transition metal dissolution, can be severely aggravated. Afterwards, we discuss representative stabilization strategies, including the surface treatment and construction of radial concentration gradients in polycrystalline secondary particles, the fabrication of rod-shaped primary particles, and the development of single-crystal NRLO cathodes. We then introduce emerging microstructural characterization techniques, especially for identification of the particle orientation, dynamic changes, and elemental distributions in NRLO microstructures. Finally, we provide perspectives on the remaining challenges and opportunities for the development of stable NRLO cathodes for the zero-carbon future.

Advancements and Challenges in High-Capacity Ni-Rich Cathode Materials for Lithium-Ion Batteries

Nowadays, lithium-ion batteries are undoubtedly known as the most promising rechargeable batteries. However, these batteries face some big challenges, like not having enough energy and not lasting long enough, that should be addressed. Ternary Ni-rich Li[NixCoyMnz]O2 and Li[NixCoyAlz]O2 cathode materials stand as the ideal candidate for a cathode active material to achieve high capacity and energy density, low manufacturing cost, and high operating voltage. However, capacity gain from Ni enrichment is nullified by the concurrent fast capacity fading because of issues such as gas evolution, microcracks propagation and pulverization, phase transition, electrolyte decomposition, cation mixing, and dissolution of transition metals at high operating voltage, which hinders their commercialization. In order to tackle these problems, researchers conducted many strategies, including elemental doping, surface coating, and particle engineering. This review paper mainly talks about origins of problems and their mechanisms leading to electrochemical performance deterioration for Ni-rich cathode materials and modification approaches to address the problems.

TiO2-LiF composite coating for improving NCM622 cathode cycling stability: one-step construction

The Ni-rich NCM622 is a promising cathode material for future high energy lithium ion batteries, but unstable electrochemical performance of NCM622 hinder its large scale commercial application. The cycling peformance of nickel-rich LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode materials can be improved by surface coating. Here, a one-step approach based on TiF4 is used to successfully manufacture modified NCM622 cathode materials with a TiO2-LiF coating. The TiO2-LiF coated NCM622 preserves 79.7% capacity retention which is higher than the pure NCM622 (68.9%) at 1C after 200 cycles within 2.7-4.3 V. This material serves as the cathode for lithium-ion batteries (LIBs). The uniform TiO2-LiF coating layer can alleviate structural degradation brought on by unfavorable side reactions with the electrolyte has been validated. TiO2-LiF coated on NCM622 cathode materials can be modified easily by one-step approach.

Recent progress on the low and high temperature performance of nanoscale engineered Li-ion battery cathode materials

Lithium ion batteries (LIB) are the domain power house that gratifies the growing energy needs of the modern society. Statistical records highlight the future demand of LIB for transportation and other high energy applications. Cathodes play a significant role in enhancement of electrochemical performance of a battery, especially in terms of energy density. Therefore, numerous innovative studies have been reported for the development of new cathode materials as well as improving the performance of existing ones. Literature designate stable cathode-electrolyte interface (CEI) is vital for safe and prolonged high performance of LIBs at different cycling conditions. Considering the context, many groups shed light on stabilizing the CEI with different strategies like surface coating, surface doping and electrolyte modulation. Local temperature variation across the globe is another major factor that influences the application and deployment of LIB chemistries. In this review, we discuss the importance of nano-scale engineering strategies on different class of cathode materials for their improved CEI and hence their low and high temperature performances. Based on the literature reviewed, the best nano-scale engineering strategies investigated for each cathode material have been identified and described. Finally, we discuss the advantages, limitations and future directions for enabling high performance cathode materials for a wide range of applications.

Synergistic Inorganic-Organic Dual-Additive Electrolytes Enable Practical High-Voltage Lithium-Ion Batteries

Severe electrolyte decomposition under high voltage can easily lead to degradation of the performance of lithium-ion batteries, which has become a major obstacle to the practical application of high-energy-density batteries. To solve these problems, a dual-functional electrolyte additive comprising inorganic lithium difluorophosphate (LiDFP) and organic 1,3,6-hexanetrinitrile (HTN) was designed and employed to improve the performance of high-voltage Si@C/LiNi_0.5Mn_1.5O₄ full batteries. LiDFP with a lower LUMO energy than the solvent in the electrolyte takes priority in reduction, facilitating the formation of a dense and stable film on the anode, effectively suppressing side reactions of the electrolyte and aiding tolerance to the volume expansion of the Si@C electrode. Additionally, the lower HOMO energy of HTN can improve the oxidation resistance of the electrolyte, with the C≡N functional group of HTN helping to remove the trace water and the byproduct HF from the electrolyte. The Si@C/LiNi_0.5Mn_1.5O₄ full battery with 1 wt % LiDFP and 1 wt % HTN in 1.0 M LiPF₆ traditional electrolyte delivers high capacity retention of 91.57% after 150 cycles at 0.2C, compared to 34.58% capacity retention without any additives. Moreover, the Coulombic efficiency of batteries with electrolyte additives can reach 99.75% on average, compared to their counterparts at ∼96.54%. The synergistic effect of LiDFP and HTN provides a promising strategy for enhancing the performance of high-voltage batteries for practical industrialization.

Nickel-Rich Layered Cathode Materials for Lithium-Ion Batteries

Nickel-rich layered transition metal oxides are considered as promising cathode candidates to construct next-generation lithium-ion batteries to satisfy the demands of electrical vehicles, because of the high energy density, low cost, and environment friendliness. However, some problems related to rate capability, structure stability, and safety still hamper their commercial application. In this Review, beginning with the relationships between the physicochemical properties and electrochemical performance, the underlying mechanisms of the capacity/voltage fade and the unstable structure of Ni-rich cathodes are deeply analyzed. Furthermore, the recent research progress of Ni-rich oxide cathode materials through element doping, surface modification, and structure tuning are summarized. Finally, this review concludes by discussing new insights to expand the field of Ni-rich oxides and promote practical applications.