Thermodynamic Analysis of Lithium-Ion Battery Storage System

The spinel Li4Mn5O12 has been considered as a prospective 3 V cathode material for the next generation of lithium-ion batteries (LIBs) due to its high energy density and excellent cycling stability. However, the low operating voltage (∼3 V) makes Li4Mn5O12 impractical for high-energy high-power LIBs. To address this issue, Ni and Fe dual doped Li4Mn5-x-yNixFeyO12 has been prepared via a facile sol-gel method combined with post-heat-treatment. The effects of dual-cations doping on the crystal structure, morphology and electrochemical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and galvanostatic charge/discharge analysis. As a result, Li4Mn4Ni0.5Fe0.5O12 exhibits the highest reversible specific capacity of 133 mAh/g at a specific current density of 25 mA/g after 100 cycles and exhibits a significantly improved high voltage performance with corresponding capacity of ∼80 mAh/g at an average voltage of 4.7 V vs. Li/Li+ and ∼122 mAh/g at above 4.0 V. These results indicate the dual doping of Ni and Fe can effectively improve both the operating voltage and reversible specific capacity of Li4Mn5O12 with excellent cycling stability, demonstrating a promising high-voltage cathode material for high-energy high-power LIBs.

Lithium ion batteries have dominated the portable electronics market and have the potential to dominate large-scale battery applications including hybrid and electric vehicles as well as grid storage because of their high energy and power densities.[1] It is well known that conventional electrolytes (such as 1.2 M LiPF6 in EC/EMC 3/7) show poor anodic stabilities above 4.5 V versus Li/Li+.[2] However, high voltage electrolytes play an intrinsic role in many applications such as hybrid and electrical vehicles, aerospace uses and power grids. As a result, high voltage electrolytes are essential for the development of next generation lithium ion batteries. One possible solution is to develop fluorinated electrolytes which not only form kinetically stable SEI interphase, but also are resistant to oxidative decomposition due to their high oxidation potential. [3] In this work, a novel fluorinated electrolyte was introduced in a graphite-LiNi0.5Mn0.3Co0.2O2 full cell operated between 3.0 - 4.6 V. The electrolyte contains 1.0 M LiPF6 dissolved in a mixture of FEC and HFDEC solvent with 1wt % LiDFOB used as the additive. Compared to a conventional EC and EMC based electrolyte, the fluorinated electrolyte shows an excellent cycle life under a 4.6V cut off voltage. NMR and GC-MS were used to analyze the harvested electrolyte post-cycling while SEM, XPS and FTIR were employed to study the interface between the electrolyte and the bulk electrodes. Most importantly, HR-XRD and XANS were conducted to investigate and compare the cycled bulk cathode electrode in different electrolytes. To the best of our knowledge, the structural change of the cycled cathode material in different electrolytes has never been reported. Therefore, we believe this research is a crucial breakthrough for studying the interaction between the electrolyte and electrode. The methodology developed could be fundamental in the design and investigation of better electrolytes for next generation lithium ion batteries. [1]Xu, Kang. "Nonaqueous liquid electrolytes for lithium-based rechargeable batteries." Chemical reviews 104.10 (2004): 4303-4418. [2] Xu, Kang. "Electrolytes and interphases in Li-ion batteries and beyond." Chemical reviews 114.23 (2014): 11503-11618. [3] Zhang, Zhengcheng, et al. "Fluorinated electrolytes for 5 V lithium-ion battery chemistry." Energy Environ. Sci. 6.6 (2013): 1806-1810.

Atomic layer deposition of amorphous iron phosphates on carbon nanotubes as cathode materials for lithium-ion batteries

Lithium silicide (LixSi) is the lithiated form of silicon, one of the most promising anode materials for the next generation of lithium-ion batteries (LIBs). In contrast to silicon, LixSi has not been well studied. Herein we report a facile high-energy ball-milling-based synthesis of four phase-pure LixSi (x = 4.4, 3.75, 3.25, and 2.33), using hexane as the lubricant. Surprisingly, the obtained Li3.75Si phase shows significant downward shifts in all X-ray diffraction peak positions, compared with the standard. Our interpretation is that the high-energy ball-mill-synthesized Li3.75Si presents smaller internal pressures and larger lattice constants. The chemical-stability study reveals that only surface reactions occur after Li4.4Si and Li3.75Si are immersed in several battery-assembly-related chemicals. The thermal-stability study shows that Li4.4Si is stable up to 350 °C and Li3.75Si is stable up to 200 °C. This remarkable thermal stability of Li3.75Si is in stark contrast to the long-observed metastability for electrochemically synthesized Li3.75Si. The carbon encapsulation of Li4.4Si has also been studied for its potential applications in LIBs.

Li-rich manganese-based cathode materials (LRMs) are considered one of the most promising cathode materials for the next generation of lithium-ion batteries (LIBs) because of their high energy density. However, there are problems such as a capacity decay, poor rate performance, and continuous voltage drop, which seriously limit their large-scale commercial applications. In this work, Li1.2Mn0.54Co0.13Ni0.13O2 coated with Li2MoO4 with a unique spinel structure was prepared with the wet chemistry method and the subsequent calcination process. The Li2MoO4 coating layer with a spinel structure could provide a 3D Li+ transport channel, which is beneficial for improving rate performance, while protecting LRMs from electrolyte corrosion, suppressing interface side reactions, and improving cycling stability. The capacity retention rate of LRMs coated with 3 wt% Li2MoO4 increased from 69.25% to 81.85% after 100 cycles at 1 C, and the voltage attenuation decreased from 7.06 to 4.98 mV per cycle. The lower Rct also exhibited an improved rate performance. The results indicate that the Li2MoO4 coating effectively improves the cyclic stability and electrochemical performance of LRMs.

Lithium-rich manganese-based cathodes (LR) are valuable cathode materials for the next generation of lithium-ion batteries (LIBs) with high-energy density. However, the fast voltage/capacity decay on cycling is the major obstacle for the practical application induced by the less-than-ideal anionic redox reactions and structure distortion. Herein, in order to tackle these challenges, a perovskite-like La2Li0.5Co0.5O4 (LLCO) material is selected as protective surface to stabilize the Li1.2Mn0.54Ni0.13Co0.13O2 (LR) substrate through wet chemical coating method. Versatile structure/phase characterizations and electrochemical tests exhibit that the LLCO can not only minish the oxygen evolution and enhance the structure stability, but also restrain the electrolyte corrosion and increase the mechanical strength of cathode materials. Moreover, the coated LLCO with high electronic/ionic conductivity dramatically accelerates the energy storage kinetic, thereby displaying the improved rate performance. Specifically, the optimized LR@LLCO sample (1LLCO) exhibits a high capacity of 250.6 mAh·g−1 after 100 cycles at 0.1 C and excellent capacity retention of 82.6% after 200 cycles at 2 C. This work provides a new idea for the modification of LR cathodes toward commercial high-performance LIBs.

Layered Li-rich Mn-based oxides are believed to be a good candidate for cathode material in the next generation of lithium-ion batteries. However, they have some disadvantages, such as low initial coulombic efficiency, low rate capacity, and deficient cyclability. To overcome these shortcomings, various approaches, such as elemental doping, have been adopted. In this study, Al-doped Li1.21Mn0.54Ni0.125Co0.125O2 were successfully synthesized using the sol–gel method. Samples were characterized by thermal analysis (TGA/DTA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), surface-area analysis, field emission scanning electron microscopy and transmission electron microscopy (TEM). Measurements of galvanostatic charge discharge and electrochemical impedance spectroscopy were also performed to evaluate the electrochemical performance of the prepared samples. The XRD patterns showed that all the samples with the structure of 0.55Li2MnO3.0.45LiNi0.33Mn0.33Co0.33O2 had a composite material with two individual layered structures that are integrated with each other. By doping Al, the lattice parameters of the samples changed. The first discharge capacity of the Al-doped specimens was lower than that of the pristine sample. In cycling performance results, it is clear that cyclic behavior and capacity stability rate in doped samples have improved compared to the undoped sample, and in the meantime, the sample with 0.05 aluminum doping has shown the best performance. Optimal performance of the doped specimens can be related to lower load transfer resistance and better structural stability.

Silicon is a promising material for high-energy anode materials for the next generation of lithium-ion batteries. The gain in specific capacity depends highly on the quality of the Si dispersion and on the size and shape of the nano-silicon. The aim of this study is to investigate the impact of the size/shape of Si on the electrochemical performance of conventional Li-ion batteries. The scalable synthesis processes of both nanoparticles and nanowires in the 10–100 nm size range are discussed. In cycling lithium batteries, the initial specific capacity is significantly higher for nanoparticles than for nanowires. We demonstrate a linear correlation of the first Coulombic efficiency with the specific area of the Si materials. In long-term cycling tests, the electrochemical performance of the nanoparticles fades faster due to an increased internal resistance, whereas the smallest nanowires show an impressive cycling stability. Finally, the reversibility of the electrochemical processes is found to be highly dependent on the size/shape of the Si particles and its impact on lithiation depth, formation of crystalline Li15Si4 in cycling, and Li transport pathways.

Li-rich Mn-based layered oxides (LMLOs) are expected to be the most promising high-capacity cathodes for the next generation of lithium-ion batteries (LIBs). However, the poor cycling stability and kinetics performance of polycrystalline LMLOs restrict their practical applications due to the anisotropic lattice stress and crack propagation during cycling. Herein, B-doped micron-sized single-crystal Co-free LMLOs were obtained by molten-salt (LiNO3 and H3BO3)-assisted sintering. The results reveal that the low-melting-point molten salt can serve as liquid-phase media to improve the efficiency of atomic mass transfer and crystal nucleation and growth. The modified single-crystal LMLO cathodes can resist the accumulation of anisotropic stress and strain during the cycling and reduce interface side reactions, thus achieving excellent high-voltage stability and kinetics performance. The reversible specific capacity of the single crystals is 210.8 mAh g-1 at 1C with a voltage decay rate of 1.95 mV/cycle and up to 161.1 mAh g-1 at 10C with a capacity retention of 81.06% after 200 cycles.

Lithium ion batteries have enabled the portable electronics revolution that changed how we communicate and share information. They have also started to penetrate the vehicle electrification and grid storage markets, two applications that are at the core of a sustainable future. In the pursuit of higher energy densities, lower costs, and longer life, nanotechnology is regularly employed to create new materials and processes in order to achieve these goals. A wonderful example is the commercialization of the lithium iron phosphate cathode which functions as a high power material only in a nanophase form, clearly demonstrating the benefit of nanotechnology.Materials engineered at the nanoscale are expected to offer a suite of advantages: high power densities are enabled by much reduced solid-state diffusion distance; high surface area reduces the effective current density; and new material structures and compositions are stabilized by nanostructuring, leading to new charge storage mechanisms. On the other hand, the use of nanomaterials in lithium ion batteries raises significant technological challenges. Thermodynamically unstable electrode/electrolyte interfaces combined with the high surface area of nanomaterials magnify the side reactions leading to performance losses. In addition electrically connecting large amounts of nanoparticles requires the use of large amounts of conducting diluents. Nanomaterials also tend to have low tap densities and are often more expensive to produce.In order for lithium ion batteries to meet the performance and cost requirements for vehicle electrification and grid storage, they increasingly employ electrode materials with challenging reaction kinetics, such as limited ionic and electronic conductivities and complex multiphase processes. By understanding nanoscale processes and using this understanding to extend the spatial scale over which battery design can be implemented, nanotechnology is expected to play an increasingly important role in enabling these new chemistries. As illustrated by the papers in this issue, new synthesis, characterization, and computational tools will facilitate this design and enable us to identify new material systems as well as their economical production.This special issue provides a snapshot of how various aspects of nanotechnology are being integrated in lithium ion batteries. Topics covered include synthesis of nanostructured intercalation and alloy anode materials, fundamental studies of the structure and mechanisms of nanostructured cathode materials based on intercalation and conversion, nanostructured solid-state electrolytes, and hierarchical electrode materials that contain nanometer scale building blocks.AcknowledgmentsWe are grateful to all the contributors for their high-quality submissions. We also thank the editorial and production staff for their guidance in the production of this issue.*The views expressed in this article do not necessarily represent the views of the Department of Energy or the United States.

Controlled synthesis of Li1.17Ni0.21Mn0.54Co0.08O2 as a cathode material for Li ion batteries

Metal hydrides for lithium-ion battery application: A review

Lithium-ion batteries are widely used to power portable electronics because of their high energy densities and have shown great promise in enabling the electrification of transport. However, the commercially used carbonate-based electrolytes are limited by a narrow operating temperature window and suffer against next generation lithium-ion battery chemistries such as silicon-containing anodes. The lack of non-carbonate electrolyte alternatives such as ether-based electrolytes is due to undesired solvent co-intercalation that occurs with graphitic anodes. Recently, fluorinated ether solvents have become promising electrolyte solvent candidates for lithium metal batteries but their applications in other battery chemistries have not been studied. In this work, we synthesize a group of novel fluorinated ether solvents and study them as electrolyte solvents for lithium-ion batteries. Using X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (ssNMR), we show that fluorinated ether electrolytes support reversible lithium-ion intercalation into graphite without solvent co-intercalation at conventional salt concentrations. To the best of our knowledge, they are the first class of ether solvents that intrinsically suppress solvent co-intercalation without the need for high or locally high salt concentration. In full cells using graphite anode, fluorinated ether electrolytes enable much higher energy densities compared to conventional glyme ethers, and better thermal stability over carbonate electrolytes (operation up to 60°C). As single-solvent-single-salt electrolytes, they remarkably outperform carbonate electrolytes with fluoroethylene carbonate (FEC) and vinylene carbonate (VC) additives when cycled with graphite-silicon composite anodes. Using X-ray photoelectron spectroscopy (XPS), NMR and density functional theory (DFT) calculations, we show that fluorinated ethers produce a solvent-derived solid electrolyte interphase, which is likely the key to suppressing solvent co-intercalation. Rational molecular design of fluorinated ether solvents will produce novel electrolytes that enable next generation lithium-ion batteries with higher energy density and wider working temperature window.

Synthesis and electrochemical studies of 1,1’-binaphthyl-2,2’-diol for aqueous rechargeable lithium-ion battery applications

Investigation on the heat generation and heat sources of cylindrical NCM811 lithium-ion batteries