A multifunctional phosphite-containing electrolyte for 5 V-class LiNi 0.5Mn1.5O4 cathodes with superior electrochemical performance

We report a highly promising organophosphorus compound with an organic substituent, tris(trimethylsilyl)phosphite (TMSP), to improve the electrochemical performance of 5 V-class LiNi0.5Mn 1.5O4 cathode materials. Our investigation reveals that TMSP alleviates the decomposition of LiPF6 by hydrolysis, effectively eliminates HF promoting Mn/Ni dissolution from the cathode, and forms a protective layer on the cathode surface against severe electrolyte decomposition at high voltages. Remarkable improvements in the cycling stability and rate capability of high voltage cathodes were achieved in the TMSP-containing electrolyte. After 100 cycles at 60 ??C, the discharge capacity retention was 73% in the baseline electrolyte, whereas the TMSP-added electrolyte maintained 90% of its initial discharge capacity. In addition, the LiNi 0.5Mn1.5O4 cathode with TMSP delivers a superior discharge capacity of 105 mA h g-1 at a high rate of 3 C and an excellent capacity retention of 81% with a high coulombic efficiency of over 99.6% is exhibited for a graphite/LiNi0.5Mn1.5O 4 full cell after 100 cycles at 30 ??C.close8

A high-power and fast charging Li-ion battery with outstanding cycle-life

Electrochemical energy storage devices based on Li-ion cells currently power almost all electronic devices and power tools. The development of new Li-ion cell configurations by incorporating innovative functional components (electrode materials and electrolyte formulations) will allow to bring this technology beyond mobile electronics and to boost performance largely beyond the state-of-the-art. Here we demonstrate a new full Li-ion cell constituted by a high-potential cathode material, i.e. LiNi0.5Mn1.5O4, a safe nanostructured anode material, i.e. TiO2, and a composite electrolyte made by a mixture of an ionic liquid suitable for high potential applications, i.e. Pyr1,4PF6, a lithium salt, i.e. LiPF6, and standard organic carbonates. The final cell configuration is able to reversibly cycle lithium for thousands of cycles at 1000 mAg-1 and a capacity retention of 65% at cycle 2000. © 2017 The Author(s)

Aerosol Synthesis Of Cathode Materials For Li-Ion Batteries

Rapid advancement of technologies for production of next-generation Li-ion batteries will be critical to address the Nation\u27s need for clean, efficient and secure transportation system and renewable energy storage system. Advancements in materials are believed to be essential to meet the growing demand of high-performance materials for Li-ion batteries, as well as to bring down the battery cost: material cost) to a reasonable level. In the past decade, the primary focus in the Li-ion battery research has been to develop new materials, which are essential to improve the performance of the electrodes in terms of energy density, power density and cycle life. However, no single material has satisfied all the necessary criteria because there is a trade-off between energy and power in Li-ion batteries. Fortunately, by tailoring the nano-scale architectures, some of the less robust high-energy materials have yielded superior power density over their bulk materials, and these nanostructured materials have come to the forefront of the battery material research. A typical example is the Li-excess composite materials adopting nanostructured morphology. These materials can attain nearly twice the capacity of commercial LiCoO2. This high capacity has traditionally been a challenge to bulk composite materials, especially at elevated charge/discharge current density and at low temperature. Despite rapid advances in material development, to date, less attention has been placed on developing approaches to commercial scale production of materials with nano to micron features. Conventional processes such as solid-state reaction and wet-chemistry processes have notable challenges for large-scale material synthesis of nanostructured materials, including difficulty in controlling particle size, morphology and sometimes stoichiometry. They can also be energy-intensive, and have challenges associated with consistent production of uniform powders at scale-up. Motivated by the above, this work aims to develop new processes that are commercially viable for large-scale production of state-of-the-art battery materials. Aerosol synthesis is a standard industrial method for producing powders with controlled particle size. The materials producing in aerosol processes can have a variety of morphologies, from one-dimensional to three-dimensional structures. Spherical particles are desirable in the Li-ion battery industry because high packing density is required. In this research, spray pyrolysis and flame spray pyrolysis are successfully developed to produce high-quality, spherical cathode materials. These processes have many advantages over conventional processes including:: 1) the ability to consistently produce uniform porous spherical particles,: 2) low-cost,: 3) simplicity, and: 4) precise control over particle composition and crystal structure. This research will not only provide a basic understanding of the aerosol process for synthesizing nanostructured cathode materials, but also strategies for industry practice in aerosol processing of state-of-the-art battery materials. The dissertation includes the following achievements in developing an aerosol approach to synthesis of cathode materials. This work, for the first time, demonstrates the synthesis of spherical-shape spinel cathode powders using a hydrogen diffusion flame. A basic understanding of the relationship between flame temperature and structure, physical and chemical properties of the produced powder, and electrochemical system are provided. In particular, flame-made nanostructured 4 V LiMn2O4 and 5 V LiNi0.5Mn1.5O4 cathode materials have shown comparable performance to those from conventional processes. A spray pyrolysis was also developed to address the synthetic conditions for synthesizing the integrated layered-layered xLi2MnO3·(1-x)LiNi0.5Mn0.5O2 and layered-spinel Li(1.2-δ)Ni0.2Mn0.6O(2-δ/2) composite materials for high-energy Li-ion batteries. The composite materials obtained from spray pyrolysis shared some common morphological characteristics: spherical in shape, meso- to macro porous, polycrystalline, highly uniform inter- and intra-particles. In particular, the layered Li1.2Ni0.2Mn0.6O2: equivalent to 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2) material displayed the highest capacity: c.a. 250 mAhg-1) among all cathode materials ever made with spray pyrolysis. Furthermore, the nanostructured composite materials showed electrochemical performance comparable to, and in some aspect better than those materials produced via coprecipitation, the standard method of synthesis

Oxidation decomposition mechanism of fluoroethylene carbonate-based electrolytes for high-voltage lithium ion batteries: a DFT calculation and experimental study

The oxidative decomposition mechanism of fluoroethylene carbonate (FEC) used in high-voltage batteries is investigated by using density functional theory (DFT). Radical cation FEC•+ is formed from FEC by transferring one electron to electrode and the most likely decomposition products are CO2 and 2-fluoroacetaldehyde radical cation. Other possible products are CO, formaldehyde and formyl fluoride radical cations. These radical cations are surrounded by much FEC solvent and their radical center may attack the carbonyl carbon of FEC to form aldehyde and oligomers of alkyl carbonates, which is similar with the oxidative decomposition of EC. Then, our experimental result reveals that FEC-based electrolyte has rather high anodic stability. It can form a robust SEI film on the positive electrode surface, which can inhibit unwanted electrolyte solvent and LiPF6 salts decomposition, alleviate Mn/Ni dissolution and therefore, improve the coulombic efficiency and the cycling stability of high voltage LiNi0.5Mn1.5O4 positive electrodes. This work displays that FEC-based electrolyte systems have considerable potential replacement of the EC-based electrolyte for the applications in 5 V Li-ion batteries

Reversible Graphite Anode Cycling with PC-Based Electrolytes Enabled by Added Sulfur Trioxide Complexes

Pyridine sulfur trioxide (PyrSO3), trimethyl amine sulfur trioxide (Me3NSO3), and triethyl amine sulfur trioxide (Et3NSO3) complexes have been investigated as electrolyte additives for lithium ion batteries. Incorporation of 0.5 to 2.0% of the SO3 complexes into a PC/EMC (1:1 v/v) 1 M LiPF6 baseline electrolyte affords reversible cycling of graphite anodes confirming generation of a stable Solid Electrolyte Interphase (SEI). Good cycling performance is observed for graphite/LiNi0.5Mn1.5O4 cells cycled to high potential (4.8 V vs Li) containing PC based electrolyte with added SO3 complexes. Ex-situ surface analysis via X-ray Photoelectron Spectroscopy (XPS) of the anodes reveals SO3 complex reduction on the surface of the graphite anode generates a sulfur-based SEI containing sulfites, sulfide, and sulfate species. The presence of the sulfur containing species is likely critical for the stability of the SEI. Ex-situ XPS analyses of the LiNi0.5Mn1.5O4 cathodes suggest that reaction of Me3NSO3 or Et3NSO3 complexes at high potential result in the generation of a stable passivation layer which affords good capacity retention and coulombic efficiency

Enhancing the Stability of LiNio.5_{o.5}0Mn1.5_{1.5}O4_{4} by Coating with LiNbO3_{3} Solid-State Electrolyte: Novel Chemically Activated Coating Process versus Sol-Gel Method

LiNbO$_{3}$-coated LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ spinel was fabricated by two methods: using hydrogen-peroxide as activating agent and sol-gel method. The structure of the obtained cathode materials was investigated using a scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the electrochemical properties of the prepared cathodes were probed by charge-discharge studies. The morphology of the coating material on the surface and the degree of coverage of the coated particles were investigated by SEM, which showed that the surface of LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ particles is uniformly encapsulated by lithium innovate coating. The influence of the LiNbO3 coating layer on the spinel’s properties was explored, including its effect on the crystal structure and electrochemical performance. XRD studies of the obtained coated active materials revealed very small expansion or contraction of the unit cell. From the capacity retention tests a significant improvement of the electrochemical properties resulted when a novel chemically activated coating process was used. Poorer results, however, were obtained using the sol-gel method. The results also revealed that the coated materials by the new method exhibit enhanced reversibility and stability compared to the pristine and reference ones. It was shown that the morphology of the coating material and possible improvement of communication between the substrates play an important role