FEATURES OF PHASE TRANSFORMATIONS IN THE SYNTHESIS OF COMPLEX LITHIUM-CONDUCTING OXIDE MATERIALS

Lithium-ion batteries (LIB`s) are widely used in consumer electronics, mobile phones, personal computers, as well as in hybrid and electric vehicles. Liquid electrolytes, which mainly consist of aprotic organic solvents and lithium-conductive salts, are used for the transfer of lithium ions in LIB`s. However, the application of liquid electrolytes in LIB`s leads to a number of problems, the most significant of which are the risk of battery ignition during operation due to the presence of flammable organic solvents and loss of capacity due to the interaction of liquid electrolyte with electrode materials during cycling. An alternative that can ensure the safety and reliability of lithium batteries is the development of completely so­lid state batteries (SSB`s). SSB`s are not only inherently safer due to the absence of flammable organic components, but also have the potential to increase significantly the energy density. Instead of a porous separator based on polypropylene saturated with a liquid electrolyte, the SSB`s use a solid electrolyte that acts as an electrical insulator and an ionic conductor at the same time. The use of a compact solid electrolyte, which acts as a physical barrier that prevents the growth of lithium dendrites, also allows using lithium metal as the anode material. It is desirable to use oxide systems as the so­lid electrolytes for SSB`s, as they are resistant to moisture and atmospheric air. Among the lithi­um-conducting oxide materials, which exhibit relatively high lithium conductivity at a room temperature and can be used as a solid electrolyte in the completely solid-state batteries, lithium-air batteries and other electrochemical devices, the most promising materials are ones with NASICON, perovskite and garnet-type structures. The phase transformations that occur during the synthesis of complex lithium-conductive oxides, namely Li1.3Al0.3Ti1.7(PO4)3 with the NASICON-type structure, Li0.34La0.56TiO3 with the perovskite-type structure and Li6.5La3Zr1.5Nb0.5O12 with the garnet-type structure by the solid-state reactions method in an air were investigated. The optimal conditions for the synthesis of each of the above-mentioned compounds were determined.

Antioxidant behavior and tribological performance of a novel multifunctional additive in complex lithium grease

Purpose This paper aims to contrastively investigate the antioxidant behavior and tribological performance of a novel multifunctional additive (PBT) and dialkyldithiophosphate (ZDDP) in complex lithium grease (CLG). Design/methodology/approach PBT was successfully synthesized through esterification reaction. The antioxidant behavior of PBT and ZDDP was investigated by thermal analysis, and meanwhile, their tribological performance was evaluated by Optimol SRV-IV oscillating reciprocating friction and wear tester (SRV-IV test) and MRS-1J four-ball tester (Four-ball test). Furthermore, their anticorrosion ability was determined by copper strip corrosion test. Findings Four-ball tests showed that the extreme pressure property of PBT was a little inferior to that of ZDDP. Besides, all the other results demonstrated that PBT showed more superior antioxidation stability, friction-reduction and antiwear ability, as well as anticorrosion performance than ZDDP. Originality/value This work provides a study of hindered phenol derivative as a multifunctional additive in lubricant grease, which can contribute to the development of substitution of ZDDP.

High Temperature Viscous Lubricants Compatibility

The state and prospects of research in the field of compatibility of viscous lubricants are analyzed. A new stand for mixing lubricants was presented, simulating the operation of a roller bearing in a wide temperature range. A method has been developed for testing the compatibility of high-temperature lubricants in terms of thermomechanical and thermo-oxidative stability. The results of a study of the compatibility of complex lithium, super-alkaline complex sulfonate and ureate lubricants are presented.

Graphene nanoflakes as effective dopant to Li-based greases

Lithium and complex lithium greases were modified by few-layer graphene nanoflakes. Tribological tests demonstrate improvement of the lubricating characteristics, e.g. increase of the welding load and decrease of the wear scar diameter after the modification. XPS method showed occurrence tribochemical reaction between lithium 12-hydroxystearate molecules and graphene nanoflakes surface during exploitation of the grease. It was shown that graphene nanoflakes are corrosion-inactive in lubricating compositions and compatible with modern additive packages.

MODIFICATION OF LITHIUM LUBRICANTS

The aim is to study the effect of the presence of free alkalis and acids on the properties of the complex lithium greases and the choice of the optimal dispersion medium, which provides the required physicochemical characteristics of the developed grease. The dispersed phase of lithium greases studied in the polyalphaolefin oils media. It was found that the use of a mixture of polyalphaolefin oil-4 and polyalphaolefin oil-40 as a percentage of 23/77 with a total content of 83.0% provides a relatively low effective viscosity of the lubricant at low temperatures and a relatively high tensile strength at high temperature.

The Investigation on Rheology and Microstructure for Lithium Complex Grease

The rheological characteristic parameters of five lithium complex lubricating greases were determined. The comparison of rheological characteristic parameters and microstructure of the five greases was made. The results showed that the knowledge of the rheological properties of lubricating greases may contribute to reflect the change of the thickener structure. The flow transition index characterized the breaking behavior of inner structure of grease, the greater this index, the better that soap fiber structure of grease; The damping factor was shifted from a medium range towards a lower value which resulted in brittle character of sample. At a constant shear rate, the soap fiber structure of complex lithium grease is dense and uniform, apparent viscosity decline rate is small. In this sense, it is relevant to understand how the development of the soap fiber structures in the grease contributes to several functional and rheological properties of lubricating greases.

Conductive capacity and tribological properties of several carbon materials in conductive greases

Purpose The purpose of this paper is to synthesize a new kind of conductive grease which possesses a prominent conductive capacity and good tribological properties. Design/methodology/approach A two-step method was used to prepare complex lithium-based grease. Ketjen black (KB), acetylene black (AB) and carbon black (CB) were characterized by transmission electron microscope and used as lubricant additives to prepare conductive greases. Conductive capacity was evaluated by a conductivity meter, a surface volume resistivity meter and a circuit resistance meter. Tribological properties were investigated by a reciprocating friction and wear tester (MFT-R4000). The worn surfaces were analyzed by a scanning electron microscope, Raman spectroscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscope. Findings The conductive grease prepared with KB has a prominent conductive capacity at room temperature, 100°C and 150°C. Further, this conductive grease also possesses better tribological properties than AB and KB greases. When the concentration of KB is 1.8 Wt.%, the coefficient of friction and wear width reduced by 11 and 14 per cent, respectively. Originality/value This work is a new application of nanometer KB as a lubricant additive in grease, which provides a direction for preparing conductive grease. The conductivity and tribology experiments have been carried out though the variation of experiment conductions.