The high‐energy‐density, Li‐rich layered materials, i.e., xLiMO2(1‐x)Li2MnO3, are promising candidate cathode materials for electric energy storage in plug‐in hybrid electric vehicles (PHEVs) and electric vehicles (EVs). The relatively low rate capability is one of the major problems that need to be resolved for these materials. To gain insight into the key factors that limit the rate capability, in situ X‐ray absorption spectroscopy (XAS) and X‐ray diffraction (XRD) studies of the cathode material, Li1.2Ni0.15Co0.1Mn0.55O2 [0.5Li(Ni0.375Co0.25 Mn0.375)O2·0.5Li2MnO3], are carried out. The partial capacity contributed by different structural components and transition metal elements is elucidated and correlated with local structure changes. The characteristic reaction kinetics for each element are identified using a novel time‐resolved XAS technique. Direct experimental evidence is obtained showing that Mn sites have much poorer reaction kinetics both before and after the initial activation of Li2MnO3, compared to Ni and Co. These results indicate that Li2MnO3 may be the key component that limits the rate capability of Li‐rich layered materials and provide guidance for designing Li‐rich layered materials with the desired balance of energy density and rate capability for different applications.
LiCoO2, discovered as a lithium‐ion intercalation material in 1980 by Prof. John B. Goodenough, is still the dominant cathode for lithium‐ion batteries (LIBs) in the portable electronics market due to its high compacted density, high energy density, excellent cycle life and reliability. In order to satisfy the increasing energy demand of portable electronics such as smartphones and laptops, the upper cutoff voltage of LiCoO2‐based batteries has been continuously raised for achieving higher energy density. However, several detrimental issues including surface degradation, damages induced by destructive phase transitions, and inhomogeneous reactions could emerge as charging to a high voltage (>4.2 V vs Li/Li+), which leads to the rapid decay of capacity, efficiency, and cycle life. In this review, the history and recent advances of LiCoO2 are introduced, and a significant section is dedicated to the fundamental failure mechanisms of LiCoO2 at high voltages (>4.2 V vs Li/Li+). Meanwhile, the modification strategies and the development of LiCoO2‐based LIBs in industry are also discussed.
A Li/CO 2 -O 2 (2 : 1, volume ratio) battery and a Li/CO 2 battery with discharging specific capacities of 1808 mA h g À1 and 1032 mA h g À1 , respectively, are reported. Li 2 CO 3 is the main discharge product in the Li/CO 2 -O 2 (2 : 1) battery and can be decomposed during charging. In the Li/CO 2 battery, the main discharge products could be Li 2 CO 3 and carbon. Both batteries can be cycled reversibly at room temperature. Experimental sectionHigh pure anhydrous LiCF 3 SO 3 ($99.995%, Sigma Aldrich Co.) was used as received. TEGDME ($99%, Sigma Aldrich Co.) was purchased and dehydrated with 0.3 nm molecular sieves (Metrohm Ltd., Switzerland). Then, LiCF 3 SO 3 was dissolved in TEGDME in a molar ratio of 1 : 4 to form the electrolyte. The cathode composition was Ketjen Black (KB) and PTFE
Rechargeable magnesium (Mg) batteries have been attracting increasing attention recently because of the abundance of the raw material, their relatively low price and their good safety characteristics. However, rechargeable Mg batteries are still in their infancy. Therefore, alternate Mg-ion insertion anode materials are highly desirable to ultimately mass-produce rechargeable Mg batteries. In this study, we introduce the spinel Li 4 Ti 5 O 12 as an Mg-ion insertion-type anode material with a high reversible capacity of 175 mA h g À1 . This material possesses a low-strain characteristic, resulting in an excellent long-term cycle life. The proposed Mg-storage mechanism, including phase separation and transition reaction, is evaluated using advanced atomic scale scanning transmission electron microscopy techniques. This unusual Mg storage mechanism has rarely been reported for ion insertion-type electrode materials for rechargeable batteries. Our findings offer more options for the development of Mg-ion insertion materials for long-life rechargeable Mg batteries. NPG Asia Materials (2014) 6, e120; doi:10.1038/am.2014.61; published online 22 August 2014 INTRODUCTIONWith growing concern about the environment, climate change and a sustainable energy supply, studies have been focused on the development of green energy storage systems with high volumetric energy density, low price and improved safety. Compared to lithium battery systems, 1-6 rechargeable magnesium (Mg) batteries are considered to be a prospective candidate for reversible energy storage because of the great abundance of Mg resources, better chemical stability of metallic Mg in humid and oxygen-containing environments and higher volumetric capacity. [7][8][9] In particular, the increasing attention to rechargeable Mg batteries is due to the pioneering work of Aurbach's group. 10-14 Some progress has been achieved toward designing electrode materials 10,15-24 and electrolytes 25-29 for rechargeable Mg batteries. Nevertheless, rechargeable Mg batteries are still in their infancy. Therefore, alternative Mg-ion insertion anode materials are highly desirable to ultimately mass-produce rechargeable Mg-ion batteries. Recently, we have discovered the feasibility of utilizing spinel Li 4 Ti 5 O 12 , which is well known as a 'zero-strain' anode material for long-life stationary lithium-ion batteries, as an anode material for rechargeable Mg batteries. In this work, we further show that spinel Li 4 Ti 5 O 12 nanoparticles (LTO NPs) can exhibit excellent Mg storage performance under optimized conditions for rechargeable Mg batteries. This material shows a high reversible capacity of B175 mA h g À1 and superior cycling performance. By using an advanced atomic resolution scanning transmission electron
The oxygen‐K pre‐edge has been broadly used to discuss the oxygen redox states in batteries. Here, through combined experimental and in theoretical studies of a number of oxide electrodes, we conclude that the O‐K pre‐edge evolution predominantly represents the transition metal state variation, which is summarized to benchmark future research.
Ni-rich cathode materials LiNi x Co y Mn1–x–y O2 (x ≥ 0.6) have attracted much attention due to their high capacity and low cost. However, they usually suffer from rapid capacity decay and short cycle life due to their surface/interface instability, accompanied by the high Ni content. In this work, with the Ni0.9Co0.05Mn0.05(OH)2 precursor serving as a coating target, a Li-ion conductor Li2SiO3 layer was uniformly coated on Ni-rich cathode material LiNi0.9Co0.05Mn0.05O2 by a precoating and syn-lithiation method. The uniform Li2SiO3 coating layer not only improves the Li-ion diffusion kinetics of the electrode but also reduces mechanical microstrain and stabilizes the surface chemistry and structure with a strong Si–O covalent bond. These results will provide further in-depth understanding on the surface chemistry and structure stabilization mechanisms of Ni-rich cathode materials and help to develop high-capacity cathode materials for next-generation high-energy-density Li-ion batteries.
LiCoO2, which was first proposed as a cathode in 1980 by Prof. John B. Goodenough, is still one of the most popular commercial cathodes for lithium‐ion batteries. Tremendous efforts have been invested in increasing the capacity of LiCoO2 by charging to high voltage. However, a series of issues, such as structural instability and dramatic side reactions with electrolytes, can emerge as cut‐off voltage above 4.5 V (vs Li/Li+). Here, a surface modification strategy with a multilayer structure is provided, involving a Zn‐rich surface coating layer, rock‐salt phase buffer layer and surface gradient Al doping layer, to overcome the detrimental issues and achieve stable cycling of LiCoO2 at 4.6 V. The complete coating of the modification layer restrains the interfacial side reactions with electrolyte and inhibits the impedance growth. The phenomenon of quasi‐epitaxial growth demonstrates that the multilayer structure significantly reduces the lattice mismatch between host LiCoO2 and surface coating layer and enhances the stability of the Zn‐rich outside layer, which promote the long‐term effectiveness of the modification. Furthermore, the disordered rock‐salt phase layer and Al surface doping also enhance the structural stability. All of these synergistically lead to the stable cycling of LiCoO2 at 4.6 V with a capacity retention of 65.7% after 500 cycles.
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