Abstract
LiTa2PO8 (LTPO) is a new solid-state lithium ion electrolyte material reported in the latest research, which has high bulk ionic conductivity and low grain boundary ion conductivity. However, it is difficult to density with conventional sintering methods. Herein, in this work, the solid-phase synthesis method was used to prepared the LTPO solid-state electrolyte, and the influence of the amount of lithium on the structure and performance of LTPO electrolyte material was investigated. The results show that the excess Li2O does not increase other impurities and does not change the structure of the material, but the liquid phase produced by the excess Li2O can promote the elimination of interfacial pores, accelerate the direct bonding of grains and improve the ionic conductivity of grain boundary, thus improving the overall ionic conductivity of the material. Considering the volatilization of lithium and the impact of liquid phase sintering at high temperatures and the content restructuring, after adding 20 wt% excess formulation of Li2O, the resultant of LTPO density is 5.0 g/cm3, the density reaches 85.58%. As a result, the total ionic conductivity of the electrolyte is 3.28 × 10–4 S/cm at 25°C, and the Li-ion diffusion activation energy is 0.27 eV. In addition, after loading this electrolyte into a Li–Li symmetric battery, it is proved that the electrolyte has lithium ion transport performance and can be used in all-solid-state batteries. However, it is also found from cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) analysis that the interface between LTPO material and Li is unstable, and Ta5+ ions are reduced, which will be another key issue to be addressed in the future.
Highlights
All-solid-state lithium batteries are non-flammable and can effectively improve the energy density and safety performance of lithium batteries, which has aroused widespread interest among researchers
The LTPO electrolyte was synthesized by conventional solidphase reaction. according to the formula LiTa2PO8+ xLi2O (x = 0, 10, 20, 30, and 40 wt%), and corresponding excess Li2CO3 (99.5%, AR), Ta2O5 (99.5%, AR), and (NH4)2HPO4 (99.5%, AR) according to the stoichiometry of the chemical formula is used as a raw material
It shows that excessive lithium leads to the dissolution of Ta5+ ions in the structure and the formation of a dielectric phase, which is unfavorable to the improvement of the ionic conductivity of the LTPO material
Summary
All-solid-state lithium batteries are non-flammable and can effectively improve the energy density and safety performance of lithium batteries, which has aroused widespread interest among researchers. The organic polymer electrolyte is composed of the polymer matrix [polyethylene oxide (PEO), polypropylene oxide (PPO), polymethacrylic acid (PMAA), methyl ester (PMMA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF)] and lithium salts (LiClO4, LiPF6, and LiBF4), in which the lithium salt is dissolved during the polymerization In this case, a thin-film electrolyte material is constructed on the surface of collector (Long et al, 2016; Muench et al, 2016; Zhou et al, 2019). The garnet structure Li6.6La3Zr1.6Ta0.4O12 with an ion conductivity of 1.18 × 10−3 S/cm at room temperature is synthesized by using spark plasma sintering (SPS) technology (Dong et al, 2019) This type of material has ionic conductivity close to that of commonly used lithium ion electrolytes, but it is unstable and reacts with moisture and carbon dioxide in the air to form a Li2CO3 interface layer, which leads to a decline of its conductivity (Liu et al, 2018). The material is unstable to lithium, and Ti4+ will be reduced after contact with lithium (Sun et al, 2018)
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