Lithium analysis in Li-ion battery materials via a scanning electron microscopy-based approach

We performed Li analysis by reflection electron energy loss spectroscopy (REELS) with a scanning electron microscopy-based apparatus. It was possible to distinguish between Li compounds containing different transition metal elements spatially, via the spectrum imaging scheme of REELS spectra. We also acquired the Li spectrum for an Li-inserted graphite negative electrode. REELS measurements with hemispherical analyzer were performed to obtain high-quality spectra with sufficient energy resolution and compared with those from cylindrical mirror analyzer measurements; the former provided a more detailed chemical state evaluation of Li.     

Electrochemical noise of a Li-ion battery: measurement and spectral analysis

Journal of Solid State Electrochemistry - Electrochemical noise of a Li-ion battery was measured during discharge at a constant value resistor. Power spectral density spectra calculations were...     

A new approach toward improved low temperature performance of Li-ion battery

We report a new approach toward formulating an electrolyte for low temperature operation of Li-ion batteries. The core of this new approach is to use LiBF₄ salt instead of LiPF₆, which is the chosen solute in the state-of-the-art Li-ion electrolytes. We found that although LiBF₄-based electrolyte has lower ionic conductivity than the LiPF₆ analogue, it provides improved low temperature performance. In particular, at −30 °C, a Li-ion cell with 1 m (mol/kg solvent) LiBF₄ dissolved in 1:1:3 (wt.) propylene carbonate (PC)/ethylene carbonate (EC)/ethylmethyl carbonate (EMC) mixed solvent delivers as high as 86% of capacity, in comparison to that obtained at 20 °C. Whereas the counterpart one, using LiPF₆, only retains 72%. Furthermore, the cell with LiBF₄-based electrolyte shows lower polarization at −30 °C. The above results suggest that the ionic conductivity of the electrolyte is not the only limitation to the low temperature operation of Li-ion batteries. Analysis of cell impedance reveals that the improved low temperature performance by LiBF₄ arises from a reduced charge-transfer resistance.     

A Li-ion oxygen battery with Li-Si alloy anode prepared by a mechanical method

Li-O₂ battery is the leading next-generation battery system, which is known for its extremely high theoretic specific energy. However, the Li metal used in Li-O₂ batteries suffers from low Li utilization and safety hazards. In this work, as an alternative to Li anode, Li₂₁Si₅ powders, which are synthesized by an easy mechanical process, are incorporated into a Li-ion oxygen battery. The electrochemical property of the prepared battery and its cycling stability are investigated. Without electrochemical prelithiation, the pursuit of Li-Si alloy anodes in this study provides an easy and scalable strategy for preparing Li-ion oxygen batteries.     

Synthesis of NiFe2O4 with different precipitation agents for Li-ion battery anode material by co-precipitation

Journal of Solid State Electrochemistry - NiFe2O4 anode materials are prepared by chemical co-precipitation method using Na2CO3, NaOH, and Na2C2O4 as precipitants, respectively, and PEG 20000 as...     

Thermal safety and performances analysis of gel polymer electrolytes synthesized by in situ polymerization for Li-ion battery

Journal of Solid State Electrochemistry - This work obtained gel polymer electrolytes (GPEs) via in situ polymerization of methyl methacrylate (MMA) in the environment of lithium...     

In-situ imaging of Li-ion migration at interfaces in an all solid Li-ion battery

We investigated the migration of Li ions at an interface between a Li_xTi₅O₁₂ (LTO) and a solid electrolyte in an all-solid Li-ion battery. The optical reflection of LTO changes with variations in the Li content because the band structures of LTO vary with the changes in the Li content. This enables us to observe Li-ion migration in the interface between the LTO and the solid electrolyte using an optical microscope. To observe the LTO particles optically, they were coated on an indium tin oxide on a glass substrate. Variations in Li migration caused by charging/discharging were clearly observed through the changes in the reflection of the LTO. LTO changed between an insulator Li₄Ti₅O₁₂ of the spinel structure and a conductor Li₇Ti₅O₁₂ of the rock-salt structure according to the changes in the Li content. The spinel LTO has a bandgap energy of approximately 2 eV. When electron–hole pairs were generated, electric strains were produced. Surface force microscopy detected the strains and imaged the distribution of lithiation/delithiation of LTO. Interfacial conduction between a sputtered LTO and Li₃PO₄ particles was imaged with high spatial resolution.     

全固态薄膜锂/锂离子电池的研究进展

本文介绍了全固态薄膜锂/锂离子电池发展;对全固态薄膜锂/锂离子电池最近的研究进展进行了综述分析,并指出了今后研究的方向。     

Low temperature preparation of crystalline ZrO2 coatings for improved elevated-temperature performances of Li-ion battery cathodes

Ultrathin crystalline ZrO(2) nanofilms have been facilely deposited on LiMn(2)O(4) particles at 120 °C using atomic layer deposition. The ZrO(2) coating shows high crystallinity, conformality and homogeneity, which contribute to considerably improved electrochemical performance of LiMn(2)O(4) at elevated temperature in lithium-ion batteries.     

Li-ion charge storage performance of wood-derived carbon fibers@MnO as a battery anode

Wood-derived carbons have been demonstrated to have large specific capacities as the anode materials of lithium-ion batteries(LIBs). However, these carbons generally show low tap density and minor volumetric capacity because of high specific surface area and pore volume. Combination with metal oxide is one of the expected methods to alleviate the obstacles of wood-derived carbons. In this work, the composites of Mn O loaded wood-derived carbon fibers(CF@Mn O) were prepared via a simple and envir...     

Fabrication and evaluation of a polymer Li-ion battery with microporous gel electrolyte

This paper introduces an easy method for the fabrication of polymer Li-ion batteries with microporous gel electrolyte (MGE). The MGE is a multiphase electrolyte, which is composed of liquid electrolyte, gel electrolyte, and polymer matrix. The MGE not only has high ionic conductivity and good adhesion to the electrodes at low temperatures, but also retains good mechanical strength at elevated temperatures. Therefore, the MGE batteries are able to operate over a wide temperature range. During battery fabrication, the MGE is formed in situ by introducing liquid electrolyte into a swellable microporous polymer membrane and then heating or cycling the battery. In this work, the chemical compatibility of MGE with metal lithium during 60 °C storage and with LiMn₂O₄ cathode during cycling was studied. In addition, graphite/MGE/LiMn₂O₄ Li-ion batteries were made and evaluated.     

Monodisperse porous LiFePO4 microspheres for a high power Li-ion battery cathode

A novel solvothermal approach combined with high-temperature calcinations was developed to synthesize on a large scale LiFePO(4) microspheres consisting of nanoplates or nanoparticles with an open three-dimensional (3D) porous microstructure. These micro/nanostructured LiFePO(4) microspheres have a high tap density and, as electrodes, show excellent rate capability and cycle stability.     

Direct evidence of morphological changes in conversion type electrodes in Li-ion battery by acoustic emission

The charge and discharge of a Li-ion battery based on conversion type electrode material are investigated operando by acoustic emission (AE). The AE technique gives a direct evidence of both structural and morphological impacts of the electrochemical conversion reaction on the electrode. During the first discharge a huge AE energy is measured not only during the biphasic conversion process, but also during the SEI reaction. On first charge, the cumulated AE energy (CAEE) shows a significant increase, during the back conversion process, while upon further cycling the CAEE fluctuation is smoothed out, but very much reproducible. This demonstrates that a conversion reaction creates an “earthquake” in the electrode during conversion, which is correlated to a strong polarization of the electrochemical curve in the first discharge. More importantly, this study demonstrates that AE is a powerful tool to survey the real-time morphological changes and to discriminate the nature of electrochemical process in the electrode.     

Anion receptor for enhanced thermal stability of the graphite anode interface in a Li-ion battery

The thermal stability of the solid electrolyte interphase (SEI) formed on a graphite anode has been enhanced by adding an anion receptor, tris(pentafluorophenyl)borane (TPFPB), to the electrolyte. The investigated electrolyte was LiBF₄ in a 2:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). Two concentrations of TPFPB have been investigated, 0.2 and 0.8 M. Galvanostatic cycling and differential scanning calorimetry (DSC) were used to study the effect of TPFPB on the electrochemical performance and thermal stability of graphite anodes. The best performance is obtained for a graphite anode cycled in an electrolyte with 0.2 M TPFPB: cyclability is improved, and the onset temperature for the first thermally activated reaction is increased by more than 60 °C up to 140–160 °C. X-ray photoelectron spectroscopy (XPS) has been used to examine the composition of the SEI formed in the different electrolytes; the improved performance for the graphite cycled with 0.2 M TPFPB is attributed to a reduced amount of LiF in the SEI.     

Characterization of the 3-dimensional microstructure of a graphite negative electrode from a Li-ion battery

The 3-dimensional microstructure of a porous electrode from a lithium-ion battery has been characterized for the first time. We use X-ray tomography to reconstruct a 43 × 348 × 478 μm sample volume with voxel dimensions of 480 nm, subsequent division of the reconstructed volumes into sub-volumes of different sizes allow us to determine microstructural parameters as a function of sub-division size. We show that the minimum size for a representative volume element is about 43 × 60 × 60 μm for volume-specific surface area, but as large as the full sample volume for porosity and tortuosity.     

Quasi in situ XPS investigations on intercalation mechanisms in Li-ion battery materials

New concepts for Li-ion batteries are of growing interest for high-performance applications. One aim is the search for new electrode materials with superior properties and their detailed characterization. We demonstrate the application of X-ray photoelectron spectroscopy (XPS) to investigate electrode materials (LiCoO₂, LiCrMnO₄) during electrochemical cycling. The optimization of a “quasi in situ” analysis, by transferring the samples with a transport chamber from the glove box to the XPS chamber, and the reliability of the experiments performed are shown. The behavior of characteristic chemical species at the electrodes and the changes in oxidation states of LiCrMnO₄ during cycling is discussed. The formation of Cr⁶⁺ is suspected as a possible reason for irreversible capacity loss during charging up to complete Li deintercalation (approximately 5.2 V). Figure Scheme of a quasi in situ XPS experiment on Li-ion battery electrode material     

Challenges in Li-ion battery high-voltage technology and recent advances in high-voltage electrolytes

The electrolyte directly contacts the essential parts of a lithium-ion battery, and as a result, the electrochemical properties of the electrolyte have a significant impact on the voltage platform, charge discharge capacity, energy density, service life, and rate discharge performance. By raising the voltage at the charge/discharge plateau, the energy density of the battery is increased. However, this causes transition metal dissolution, irreversible phase changes of the cathode active material,...     

Comparison of condom deterioration in different pack shapes

Most condoms, especially those purchased by international aid agencies, are packed in square aluminium foil packs. The alternative rectangular packs use less packing material, and are more compact to ship and store. In this article, we describe a trial where condoms in square packs and in simulated rectangular packs were tested for physical properties after oven-conditioning for 3 months at 50 °C. We concluded that some products' inflation properties were unaffected by the pack shape. All products' tensile properties were adversely affected by a rectangular pack when a ring sample was used, but when more conventional dumbbell samples were used, the effect was quite small.     

Investigation of particle isolation in Li-ion battery electrodes using Li NMR spectroscopy

⁷Li MAS NMR spectroscopy was used to study the failure mechanisms of LiNi_0.8Co_0.15Al_0.05O₂ electrodes in Li-ion cells. Three sets of electrodes with different degrees of power fade (0%, 9% and 23%) were studied. The three electrodes were charged to various states of charge (0%, 40%, 60%, 80% and 100%) in pouch cells which were subsequently disassembled for NMR analysis. The lithium NMR shifts of the positive electrodes in the different states of charge were investigated. The results indicate that NMR spectroscopy can be used to probe particle isolation in these electrodes. Particle isolation is responsible for the capacity and power fades since some of the active material particles are disconnected from the matrix. This study also clearly showed the loss of electrochemically active lithium as the power fade increased.     

Enhanced graphite passivation in Li-ion battery electrolytes containing disiloxane-type additive/co-solvent

This article reports the synthesis details and film-forming properties of 1,1,3,3-tetramethyl-1,3-bis(3-(ω-hexadecyloxy-deca(ethylenoxy)propyl)disiloxane, a new potential electrolyte additive/functional co-solvent for propylene carbonate (PC)-based Li-ion cells with graphitic anodes. Galvanostatic charge/discharge characteristics and scanning electron microscopy images provide direct evidence for the suppression of solvent intercalation and graphite exfoliation in the presence of the additive. In terms of irreversible capacity, the additive’s efficiency is the highest for 15% weight ratio in the solvent mixture. Potentiodynamic measurements have revealed that disiloxane component undergoes irreversible reduction at potential significantly higher then PC decomposition. Energy dispersive spectroscopy analysis of graphite flake surfaces confirm that silicon species from the disiloxane decomposition are built in the passive layer. The reported compound may be considered as a basis for alternative cost-effective electrolyte compositions for low-temperature applications.