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Abstract: In an effort to improve thermal shrinkage and electrochemical performance of a separator for a lithium-ion battery, we develop a new composite separator by introducing ceramic coating layers onto both sides of a polyethylene (PE) separator. The ceramic coating layers are comprised of SiO2 nanoparticles and polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) binders. In comparison to the dense structure of conventional nanocomposite coating layers, the ceramic coating layers are featured with close-packed SiO2 nanoparticles, which affords a well-developed porous structure, i.e. highly connected interstitial voids formed between the nanoparticles. On the basis of this structural understanding of the composite separators, the effects of ceramic coating layers on the separator properties are investigated as a function of SiO2 powder size. Owing to the existence of the heat-resistant SiO2 coating layers, the composite separators show significant reduction in thermal shrinkage than the pristine PE separator. More intriguingly, in comparison to the large-sized (=530nm) SiO2, the small-sized (=40nm) SiO2 offers a large number of SiO2 nanoparticles in the ceramic coating layers, high porosity contributing to facile ion transport, and small increase in the cell impedance, which consequently allows substantial improvements in cell performances as well as thermal shrinkage of the separator. [Copyright &y& Elsevier]

Abstract: A unique approach for improving the thermal stability of delithiated LiCoO2 cathodes has been presented, which is based on the encapsulation of LiCoO2 by a new cyano-substituted polyvinylalcohol (cPVA)-based gel polymer electrolyte. In a bid to maximize the effect of encapsulation, the cPVA-based gel polymer electrolyte was applied to the LiCoO2 cathode with a predetermined degree of porosity. Through this new process, the gel polymer electrolyte is expected to locate preferentially onto the LiCoO2 at well-controlled thickness, with the overall porous structure of the modified cathode being little influenced. Due to the presence of cyano (s, the cPVA shows high dielectric constant (ɛ =15 at 1kHz at 20°C), which is thus expected to enhance the Li-salt dissociation, leading to the excellent ionic conductivity (around 7mScm at 25°C). Under the assumption that the LiCoO2 could be fully covered with the cPVA, the encapsulated thickness is calculated around 10nm, which was further evidenced by the FE-SEM results. Meanwhile, compared to the pristine LiCoO2 cathode (ΔH =413Jg−1), the modified LiCoO2 cathode exhibited the superior thermal stability (ΔH =31Jg−1) and also presented the satisfactory C-rate performances and cyclability. Such a remarkable enhancement in the thermal stability and the electrochemical performances has been discussed on the basis of the morphology of the modified LiCoO2 cathode and the electrochemical properties of the cPVA-based gel polymer electrolytes. [Copyright &y& Elsevier]

Abstract: A unique approach for improving the thermal stability of LiCoO2 cathode is presented, which is based on the treatment of LiCoO2 with ionic liquid (BDMIPF6, butyldimethylimidazolium-hexafluorophosphate), instead of traditional electrolyte modification. The electrolyte modification by the BDMIPF6 addition deteriorates the C-rate performances especially at high charge/discharge rates, with slightly improving the exothermic reaction between delithiated (charged) LiCoO2 and electrolytes. On the other hand, the BDMIPF6-modified cathode noticeably improves the thermal stability as well as little changes the C-rate performances. This is believed mainly due to the preferential location of BDMIPF6 in the LiCoO2 cathode rather than in the carbon anode, which might make it possible that the BDMIPF6 could effectively contribute to the suppression of exothermic reaction of delithiated LiCoO2 with electrolytes, with little affecting the electrolyte and the carbon anode. [Copyright &y& Elsevier]

Abstract: We have previously demonstrated polyimide (PI) gel polymer electrolyte (GPE)-based nanoencapsulation as a new surface modification strategy for high-voltage cathode materials. In this study, in an endeavor to attain a more comprehensive understanding of the PI GPE-based surface modification, effects of structural variation of PI encapsulating layers (specifically, focusing on PI coating thickness) on cell performance and thermal stability of high-voltage (4.4 V) LiCoO2 are investigated. Herein, PI coating thickness is tuned between approximately 10 and 40 nm by varying polyamic acid (synthesized from pyromellitic dianhydride/oxydianiline) concentration of coating solutions. As PI coating thickness is increased, discharge C-rate capability of cells is deteriorated due to undesired rise of ionic and electronic resistance of thick PI coating layers. On the other hand, thick PI encapsulating layers are effective in mitigating interfacial exothermic reaction between delithiated LiCoO2 and liquid electrolyte. Notably, among the various PI coating thicknesses, average thickness of 10 nm imparts well-balanced enhancement in cell performance and thermal stability. These results demonstrate that structural fine-tuning (particularly, coating thickness) of PI encapsulating layers, acting as ion-conductive protective conformal thin films, plays a significant role in optimizing their beneficial coating effects on high voltage LiCoO2. [Copyright &y& Elsevier]

Abstract: As a facile and scalable approach to the surface modification of high-voltage cathode materials for lithium-ion batteries, direct UV-assisted conformal coating of poly(tris(2-(acryloyloxy)ethyl) phosphate) (PTAEP) gel polymer electrolyte on as-formed LiNi1/3Co1/3Mn1/3O2 (NCM) cathode is presented. The smooth and continuous PTAEP coating layer with nanometer-thickness (∼20 nm) is successfully introduced on the NCM surface without impairing electronic/ionic conduction pathways preformed in the NCM cathode. Owing to this structural uniqueness, the PTAEP-coated NCM cathode significantly improves the high-voltage (4.6 V) cycling performance and mitigates the exothermic reaction between the delithiated NCM and liquid electrolyte. This demonstrates that the conformal PTAEP nanocoating layer proposed herein, which is completely different from conventional inorganic material-based coating layers, acts as a new ion-conductive protective film that effectively suppresses unwanted interfacial side reactions between the high-voltage cathode materials and liquid electrolyte. [Copyright &y& Elsevier]

Abstract: Herein, we report on a novel precipitation method to enable LiMnPO4 olivine (LMP) as a cathode material for lithium ion batteries (LIBs) to reach high capacity at high discharge rates. By confining Mn3(PO4)2 precipitation on surface of a precursor seed of Li3PO4, the size of LMP particles is limited to less than 100nm for a smaller dimension. The cathode material delivers discharge capacities of 145mAhg−1 at 0.1C, 112mAhg−1 at 1C to 62mAhg−1 at 5C (comparable with top three performances ). Even if precipitation is one of the versatile strategies to prepare the cathode material, it has not been reported that such a first-tier high performance is obtained from LMP prepared by precipitation methods. When compared with LMP particles synthesized by a conventional co-precipitation method, the performances are recognized to be considerably enhanced. Also, the surface-confined precipitation process described in this work does not involve a ball milling step with a conductive agent such as carbon black so that a low cost synthesis is feasible. [Copyright &y& Elsevier]

Abstract: In an endeavour to improve not only the thermal shrinkage but also the electrochemical performance of separators in lithium-ion batteries, a novel composite separator is developed, i.e., a close-packed SiO2/poly(methyl methacrylate) (PMMA) binary nanoparticles-coated polyethylene (PE) separator. The introduction of SiO2 nanoparticles to the coating layer effectively suppresses thermal shrinkage of the composite separator. In contrast to a SiO2/PMMA coating layer having a film-shaped PMMA binder, the SiO2/PMMA binary nanoparticle coating layer employs PMMA particles as a binder. As a consequence, a highly porous structure, i.e., well-connected interstitial voids, is formed between the binary SiO2 and PMMA nanoparticles. The unique porous morphology allows favourable liquid electrolyte wettability and facile ionic conduction, which play a crucial role in improving cell performance such as the discharge capacity and the C-rate capability of the composite separator. [ABSTRACT FROM AUTHOR]

Abstract: To improve the thermal shrinkage of the separators that are essential to securing the electrical isolation between electrodes in lithium-ion batteries, we develop a new separator based on a ceramic composite membrane. Introduction of microporous, ceramic coating layers onto both sides of a polyethylene (PE) separator allows such a progress. The ceramic coating layers consist of nano-sized alumina (Al2O3) powders and polymeric binders (PVdF-HFP). The microporous structure of the ceramic coating layers is observed to be crucial to governing the thermal shrinkage as well as the ionic transport of the ceramic composite separators. This microporous structure is determined by controlling the phase inversion, more specifically, nonsolvent (water) contents in the coating solutions. To provide a theoretical basis for this approach, a pre-investigation on the phase diagram for a ternary mixture comprising PVdF-HFP, acetone, and water is conducted. On the basis of this observation, the effect of phase inversion on the morphology and air permeability (i.e. Gurley value) of ceramic coating layers is systematically discussed. In addition, to explore the application of ceramic composite separators to lithium-ion batteries, the influence of the structural change in the coating layers on the thermal shrinkage and electrochemical performance of the separators is quantitatively identified. [Copyright &y& Elsevier]