Rivalry at the Interface: Ion Desolvation and Electrolyte Degradation in Model Ethylene Carbonate Complexes of Li+, Na+, and Mg2+ with PF6– on the Li4Ti5O12 (111) Surface
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ABSTRACT:
SUBMITTER: Rasheev H
PROVIDER: S-EPMC8582039 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The density, microstructure, and ionic conductivity of solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 (LATP) ceramics prepared by cold sintering using liquid and solid sintering additives are studied. The effects of both liquid (water and water solutions of acetic acid and lithium hydroxide) and solid (lithium acetate) additives on densification are investigated. The properties of cold-sintered LATP are compared to those of conventionally sintered LATP. The materials cold-sintered at temperatures 140-280 °C and pressures 510-600 MPa show relative density in the range of 90-98% of LATP's theoretical value, comparable or higher than the density of conventionally sintered ceramics. With the relative density of 94%, a total ionic conductivity of 1.26 × 10-5 S/cm (room temperature) is achieved by cold sintering at the temperature of 200 °C and uniaxial pressure of 510 MPa using water as additive. The lower ionic conductivities of the cold-sintered ceramics compared to those prepared by conventional sintering are attributed to the formation of amorphous secondary phases in the intergranular regions depending on the type of additives used and on the processing conditions selected.
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Project description:Samples of Li4Ti5O12-y solid solutions are synthesized by one-step solid-state carbothermal reduction reaction using Li2CO3, anatase, and carbon black under a nitrogen atmosphere. The underlying formation mechanism that leads to Li4Ti5O12-y solid solutions is proposed. The formation mechanism of the Li4Ti5O12-y solid solution is investigated by in situ variable temperature X-Ray diffraction (VT-XRD) and thermogravimetric analysis/differential scanning calorimetry (TGA-DSC). First, some Ti4+ centers are converted to Ti3+ (TiO2-TiO2-x) because of the presence of carbon black. Secondly, Li2CO3 reacts with TiO2-x (anatase) to form Li2TiO3. Thirdly, Li2TiO3 reacts with TiO2-x to form the Li4Ti5O12-y solid solution, while anatase starts to transform into rutile at the same time. Rutile reacts with Li2TiO3 to form Li4Ti5O12-y at higher temperatures. The presence of Ti3+ not only improves the electrical conductivity but also improves the ionic conductivity. As a result, the as-prepared material exhibits good rate capability and cycling stability with 99.3% capacity retention after 200 cycles.
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Project description:Materials with high-power charge-discharge capabilities are of interest to overcome the power limitations of conventional Li-ion batteries. In this study, a unique solvothermal synthesis of Li4Ti5O12 nanoparticles is proposed by using an off-stoichiometric precursor ratio. A Li-deficient off-stoichiometry leads to the coexistence of phase-separated crystalline nanoparticles of Li4Ti5O12 and TiO2 exhibiting reasonable high-rate performances. However, after the solvothermal process, an extended aging of the hydrolyzed solution leads to the formation of a Li4Ti5O12 nanoplate-like structure with a self-assembled disordered surface layer without crystalline TiO2. The Li4Ti5O12 nanoplates with the disordered surface layer deliver ultrahigh-rate performances for both charging and discharging in the range of 50-300C and reversible capacities of 156 and 113 mAh g-1 at these two rates, respectively. Furthermore, the electrode exhibits an ultrahigh-charging-rate capability up to 1200C (60 mAh g-1; discharge limited to 100C). Unlike previously reported high-rate half cells, we demonstrate a high-power Li-ion battery by coupling Li4Ti5O12 with a high-rate LiMn2O4 cathode. The full cell exhibits ultrafast charging/discharging for 140 and 12 s while retaining 97 and 66% of the anode theoretical capacity, respectively. Room- (25 °C), low- (- 10 °C), and high- (55 °C) temperature cycling data show the wide temperature operation range of the cell at a high rate of 100C.
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Project description:Bulk-type all-solid-state batteries (ASSBs) consisting of composite electrodes of homogeneously mixed fine particles of both active materials and solid electrolytes (SEs) exhibit a high safety, high energy density, and long cycle life. SE nanoparticles are required for the construction of ion-conducting pathways as a response to the particle size reduction of active materials; however, simple and low-cost milling processes for producing nanoparticles cause a collapse in the crystal structure and eventually amorphization, decreasing the conductivity. This study develops a heat treatment process in water vapor for the low-temperature crystallization of ultrafine SE amorphous particles and the size control of crystalline nanoparticles. An ultrafine (approximately 5 nm) amorphous powder of Li1.3Al0.3Ti1.7(PO4)3 (LATP), as a typical oxide-type SE, is produced via wet planetary ball milling in ethanol. The water vapor induces a rearrangement of the crystal framework in LATP and accelerates crystallization at a lower temperature than that in air. Further, since particle growth is also promoted by water vapor, depending on the heating temperature and time, this heat treatment process can be also applied to the size control of crystalline LATP nanoparticles. A combination of the wet planetary ball milling and heat treatment in water vapor will accelerate the practical application of bulk-type ASSBs.
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Project description:In Li-ion batteries (LIBs), a memory effect has been revealed in two-phase electrode materials such as olivine LiFePO4 and anatase TiO2, which complicates the two-phase transition and influences the estimation of the state of charge. Practical electrode materials are usually optimized by the element doping strategy, however, its impact on the memory effect has not been reported yet. Here we firstly present the doping-induced memory effect in LIBs. Pristine Li4Ti5O12 is free from the memory effect, while a distinct memory effect could be induced by Al-doping. After being discharged to a lower cutoff potential, Al-doped Li4Ti5O12 exhibits poorer electrochemical kinetics, delivering a larger overpotential during the charging process. This dependence of the overpotential on the discharging cutoff leads to the memory effect in Al-doped Li4Ti5O12. Our discovery emphasizes the impact of element doping on the memory effect of electrode materials, and thus has implications for battery design.
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Project description:Perovskite La2/3xLi3xTiO3 (LLTO) materials are promising solid-state electrolytes for lithium metal batteries (LMBs) due to their intrinsic fire-resistance, high bulk ionic conductivity, and wide electrochemical window. However, their commercialization is hampered by high interfacial resistance, dendrite formation, and instability against Li metal. To address these challenges, we first prepared highly dense LLTO pellets with enhanced microstructure and high bulk ionic conductivity of 2.1×10-4 S cm-1 at room temperature. Then, the LLTO pellets were coated with three polymer-based interfacial layers, including pure (polyethylene oxide) (PEO), dry polymer electrolyte of PEO-LITFSI (lithium bis (trifluoromethanesulfonyl) imide) (PL), and gel PEO-LiTFSI-SN (succinonitrile) (PLS). It is found that each layer has impacted the interface differently; the soft PLS gel layer significantly reduced the total resistance of LLTO to a low value of 84.88 Ω cm-2. Interestingly, PLS layer has shown excellent ionic conductivity but performs inferior in symmetric Li cells. On the other hand, the PL layer significantly reduces lithium nucleation overpotential and shows a stable voltage profile after 20 cycles without any sign of Li dendrite formation. This work demonstrates that LLTO electrolytes with denser microstructure could reduce the interfacial resistance and when combined with polymeric interfaces show improved chemical stability against Li metal.
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