This book addresses the comprehensive understanding of Ni-rich layered oxide of lithium-ion batteries cathodes materials, especially focusing on the effect of dopant on the intrinsic and extrinsic effect to its host materials. This book can be divided into three parts, that is, 1. overall understanding of layered oxide system, 2. intrinsic effect of dopant on layered oxides, and 3. extrinsic effect of dopant on layered oxides. To truly understand and discover the fundamental solution (e.g. doping) to improve the Ni-rich layered oxides cathodic performance, understanding the foundation of layered oxide degradation mechanism is the key, thus, the first chapter focuses on discovering the true degradation mechanisms of layered oxides systems. Then, the second and third chapter deals with the effect of dopant on alleviating the fundamental degradation mechanism of Ni-rich layered oxides, which we believe is the first insight ever been provided. The content described in this book will provide research insight to develop high-performance Ni-rich layered oxide cathode materials and serve as a guide for those who study energy storage systems. ​

The growing demand for rechargeable Li-ion batteries with higher performance metrics has spurred intensive research efforts. In the quest for safe and low-cost cathode materials with desirable energy/power capabilities, high-nickel layered oxides (LiNi [subscript 1- x] M [subscript x] O2; x 0.5, M = Co, Mn, Al) are among the most promising candidates. However, limited cycle/calendar life especially at elevated temperatures and poor thermal-abuse tolerance are serious challenges for their practical applications. This dissertation focuses on the fundamental understanding of electrode-electrolyte incompatibility for high-Ni LiNi [subscript 1-x] M [subscript x] O2 with state-of-the-art nonaqueous electrolytes at deep charge during battery operation, and corresponding strategies for inhibiting the associated unwanted parasitic reactions and enabling excellent cyclability/safety in practical cell configurations. First, we reveal the dynamic behaviors of the CEI on LiNi [subscript 0.7] Co [subscript 0.15] Mn [subscript 0.15] O2 driven by conductive carbon in composite electrodes. Secondary-ion mass spectrometry (SIMS) shows that the CEI, initially formed on carbon black from spontaneous reactions with the electrolyte prior to cell operation, passivates the cathode through a mutual exchange of surface species. By tuning the CEI thickness, we demonstrate its impact on the evolution of the electrode-electrolyte interface during cell operation at high voltages. Next, we study the evolution of the SEI on anodes, where metallic Li deposition causes capacity fade and safety issues. On graphite harvested from pouch cells paired with LiNi [subscript 0.61] Co [subscript 0.12] Mn [subscript 0.27] O2 after 3,000 cycles, SIMS reveals large Li deposition in the SEI, triggered by transition-metal cations dissolved from the cathode and migrated to the anode. With Al doping (~1 mol %) in LiNi [subscript 0.61] Co [subscript 0.12] Mn [subscript 0.27] O2, dissolution is effectively inhibited and superior long-term cyclability is achieved ( 80% after 3,000 cycles). With knowledge on both electrodes, we then conduct a comprehensive assessment on the long-term cyclability of high-Ni LiNi [subscript 0.7] Co [subscript 0.15] Mn [subscript 0.15] O2 and commercially established LiNi [subscript 0.8] Co [subscript 0.15] Al [subscript 0.05] O2 in pouch full cells (1,500 cycles). Various degradation processes leading to performance deterioration are carefully invesitgaeted. Based on the results, we identify key challenges, relative to NCA, for realizing a long service life of high-Ni NCM and corresponding mitigation strategies. Finally, we design tailored nonaqueous electrolytes based on exclusively aprotic acyclic carbonates free of ethylene carbonate (EC) and realize unusual thermal and electrochemical performance of an ultrahigh-nickel cathode (LiNi [subscript 0.94] Co [subscript 0.06] O2), reaching a specific capacity of 235 mA h g−1. By using two model electrolyte systems, we present assembled graphite|LiNi [subscript 0.94] Co [subscript 0.06] O2 pouch full cells with exceptional thermal stability, energy/power capabilities, and long service life

The ever-growing market of consumer electronics has been driving surging demand for higher-energy-density lithium-ion batteries (LIBs). Since cathode materials primarily dictate the energy density and cost, extensive investigations have been devoted to exploring advanced cathodes for high-performance LIBs. High-nickel layered oxides LiNi [subscript x] M [subscript 1-x] O2 (x ≥ 0.6, M = Co, Mn, etc.) are one of the most promising candidates and are being extensively pursued. Unfortunately, the practical applicability of high-Ni cathodes is seriously hampered by their poor cyclability, alarming susceptibility to thermal abuse, and decreased air-stability. This dissertation focuses on enhancing the stability of high-Ni cathodes with diverse strategies and advancing the scientific comprehension of high-Ni cathode materials. First, the effect of pillaring Mg-ion doping in the high-Ni cathode LiNi0.94Co0.06O2 is investigated. The incorporation of Mg greatly suppresses the anisotropic lattice collapse and maintains the integrity of cathode particles upon high-voltage cycling, significantly enhancing the cyclability. More importantly, the thermal stability of high-Ni cathodes is notably improved by Mg doping. Second, boron-based polyanion is employed to tune high-Ni cathodes. The introduction of boron-based polyanion enables a well-passivated boron/phosphorus-rich cathode-electrolyte interphase, which alleviates electrolyte corrosion on high-Ni cathodes and thus improves the cyclability. Meanwhile, the boron-based polyanion improves the air stability of high-Ni cathodes as well. Third, a well-designed phosphoric acid treatment approach is presented to modify the high-Ni cathode LiNi0.94Co0.06O2. The implemented treatment not only reduces the detrimental surface residual lithium, but also remarkably improves the electrochemical performance and long-term air-storage stability. Via a range of advanced analytical techniques, the underlying mechanisms involved on the improved performance are disclosed from interphasial and structural perspectives at the nanoscale. Finally, a comparative study is performed to unveil the stabilities of LiNi [subscript 1-x-y] Mn [subscript x] Co [subscript y] O2 (NMC) cathodes with different Ni contents at identical degrees of delithiation. The overall stabilities of two representative cathodes, LiNi0.8Mn0.1Co0.1O2 and LiNiO2, are evaluated with a rigorous control of an identical 70 mol % delithiation. The results suggest that NMC cathodes with higher-Ni contents may have better overall stability than low-Ni NMC cathodes at a given degree of delithiation, disparate from the prevailing belief that high-Ni cathodes with higher-Ni content have inherently reduced stabilities

The worldwide electrification of the automobile industry has been strongly pushing the advancement of lithium-ion batteries (LIBs) with high energy density and long service life. Since the cathode is currently the limiting electrode for energy density, safety, and cost of commercial LIBs, extensive efforts have been devoted into investigating next-generation high-performance cathode materials with high capacity and operating voltage. Among the pool of cathodes, high-nickel layered oxide cathodes, LiNixM1−xO2 (M = Co, Mn, Al, etc.; x > 0.7), are regarded as one of the most promising candidates. However, the practical viability of high-Ni cathodes is compromised by their air instability, fast structural and interfacial deteriorations during operation, poor thermal stability, and high cost. On the other hand, another promising cathode, high-voltage spinel LiNi0.5Mn1.5O4, exhibits better thermal and structural stabilities, but suffers from rapid performance degradations due to its high operating voltage of > 4.7 V vs. Li+/Li. This dissertation focuses on stabilizing the operation of high-Ni and high-voltage spinel cathodes with diverse modification strategies and advancing the understanding of the degradation mechanisms of cells with high-voltage cathodes assisted by state-of-the-art characterizations. First, the function of atomic scale zinc-doping in a high-Ni cathode LiNi0.94Co0.04Zn0.02O1.99 is investigated. The incorporation of Zn greatly mitigates the average voltage and capacity fade by ameliorating the anisotropic lattice distortion, enhancing the structural integrity, and reducing cathode-electrolyte side reactions. Moreover, Zn-doping is proved beneficial to improve the thermal stability. Second, a cobalt- and manganese-free LiNi0.93Al0.05Ti0.01Mg0.01O2 cathode is rationally designed, synthesized, and comprehensively investigated. Collectively, the use of Al, Ti, and Mg in the cathode enables a stable operation of practical full cells over 800 cycles by alleviating electrolyte decomposition reactions, transition-metal crossover, and active lithium loss. Third, single-element doped cathodes, viz., LiNi0.95Co0.05O2, LiNi0.95Mn0.05O2, and LiNi0.95Al0.05O2, along with undoped LiNiO2, are compared through a control of cutoff energy density to elucidate the role of dopants in high-Ni cathodes. Via a group of advanced analytical techniques, it is unveiled that one critical role of dopant is regulating the state-of-charge and the occurrence of H2–H3 phase transition of high-Ni cathodes, which essentially dictates the cycle stability. Finally, electrochemical modifications on the graphite anode and high-voltage spinel cathode are performed and characterized. The results suggest that the graphite anode interphase degradations caused by acidic and transition-metal crossover species generated from the cathode predominately contribute to the cell performance deterioration. Based on in-depth analyses, pathways towards long-life high-voltage full cells are pictured

The thriving energy-storage market has been motivating enormous efforts to advance the state-of-art lithium-ion batteries. The development of cathode materials, in particular, holds the key to realizing the high-energy-density and low-cost promise. Among the insertion-reaction cathodes currently in play, the layered oxides, especially the LiNiO2-based high-Ni type, are being intensively pursued as one of the most promising candidates. However, the high-Ni layered oxides inherently encounter a trade-off between capacity and stability – the higher the capacity contributed by the higher Ni content, the worse the electrochemical cyclability. This dissertation focuses on improving the stability of high-Ni layered oxide cathodes through multiple effective approaches. First, a practical doping method is presented by incorporating a small dose of Al into the layered structure, which significantly improves the electrochemical performance of the cathode. It reveals that Al-incorporation greatly enhances the stability of cathode-electrolyte-interphase (CEI) due to the modified cathode electronic structure. Furthermore, in-situ X-ray diffraction provides an operando evidence for the reduced lattice distortions during cycling with Al-incorporation. Second, lithium bis(oxalate) is employed as an effective electrolyte additive to improve the electrode-electrolyte-interphase stability. The well-tuned electrode-electrolyte interphase is featured with excellent robustness against electrochemical abuse. Moreover, the correlation between cathode-surface chemistry and anode-electrolyte interphase is revealed by studying the interphases at atomic level. Third, by constructing a dual-functional binder framework with a conductive polymer polyaniline, the high-Ni layered oxide cathodes exhibit significantly improved cyclability. This new binder framework not only promotes the rate performance even at low temperatures, but also effectively scavenges the acidic species in the electrolyte through a protonation process. Hence the cathode-surface reactivity is greatly suppressed and the rock-salt phase propagation into the bulk structure is considerably alleviated. Finally, in comparing with the state-of-art cathode (LiNi [subscript 0.8] Co [subscript 0.1] Mn [subscript 0.1] O2), the interphasial and structural evolution processes of high-Ni layered oxides (LiNi [subscript 0.94] Co [subscript 0.06] O2) are systematically investigated over the course of their service life (1,500 cycles). By applying advanced analytical techniques (e.g., Li-isotope labeling and region-of-interest method), the dynamic chemical evolution on the cathode surface is revealed with spatial resolution, and the correlation between lattice distortion and cathode-surface reactivity is established for the first time

Metallic lithium has been considered one of the most attractive anode materials for high-energy batteries because it has a low density (0.53 g cm8́23), the lowest reduction potential (8́23.04 V vs. the standard hydrogen electrode), and a high theoretical specific capacity (3,860 mAh g8́21). Chalcogen elements, such as sulfur and selenium, have been widely reported as promising cathode candidates for next-generation lithium-metal batteries (LMBs) that demonstrate much higher energy density than current lithium-ion batteries. However, lithium0́3chalcogen batteries still suffer from the loss of cathode active materials and the degradation of lithium metal anode owing to the shuttle effects of intermediate products (e.g., polysulfides and polyselenides), leading to fast capacity fading and poor cyclability. Moreover, for lithium metal anodes, the cracking of solid electrolyte interphase (SEI) layer during long cycling results in dead lithium formation and lithium dendrite growth, leading to poor Coulombic efficiency and potential safety issues. The abovementioned challenges hinder the commercialization of LMBs. To address these problems, various strategies have been developed to mitigate the dissolution/diffusion of redox intermediates and stabilize metallic lithium anodes. In this dissertation, sulfur- and selenium-based nanocomposites were synthesized and employed as advanced cathode materials for high-energy LMBs. The correlations between syntheses, properties, and performances of such chalcogen cathode materials were established by various characterization methods such as microstructural analyses, solid-state nuclear magnetic resonance, X-ray photoelectron spectroscopy, and nanoscale X-ray computed tomography. Additionally, the interfacial electrochemistry of lithium metal anodes and ionic liquid0́3based electrolytes is comprehensively investigated, revealing the effective stabilization and protection of lithium anode via the formation of an in situ SEI layer with specific compositions. Moreover, strategies for achieving novel solid polymer electrolytes with improved lithium-ion transference number were demonstrated, paving the way toward safe LMBs by mitigating lithium dendrite growth. This dissertation provides a combined strategy of advanced cathode design, electrolyte engineering, and lithium anode stabilization to develop high-energy LMBs for practical applications.

Lattice oxygen can play an intriguing role in electrochemical processes, not only maintaining structural stability, but also influencing electron and ion transport properties in high-capacity oxide cathode materials for Li-ion batteries. We report the design of a gas-solid interface reaction to achieve delicate control of oxygen activity through uniformly creating oxygen vacancies without affecting structural integrity of Li-rich layered oxides. Furthermore, theoretical calculations and experimental characterizations demonstrate that oxygen vacancies provide a favourable ionic diffusion environment in the bulk and significantly suppress gas release from the surface. The target material is achievable in delivering a discharge capacity as high as 301 mAh g-1 with initial Coulombic efficiency of 93.2%. After 100 cycles, a reversible capacity of 300 mAh g-1 still remains without any obvious decay in voltage. Our study sheds light on the comprehensive design and control of oxygen activity in transition-metal-oxide systems for next-generation Li-ion batteries.