Chen Hongzhu,Li Zhicheng,Chen Jiahao,Xia Enjie,Wu Yanmei,Zhang Hong
Lithium-ion batteries (LIBs) based on solid-state electrolytes have attracted much attention for their high safety and energy density. Li 29 Zr 9 Nb 3 O 40 (LZNO), as a new kind of Li-ion conductor, has great potential in applications of solid-state LIBs. In this work, various contents of LiF are selected to modify LZNO Li-ion conductor, and the optimal content of LiF is 5 wt% (weight%). The phase component, crystal structure, ionic conductivity, and electrochemical performance are investigated. The refinement of crystallographic information based on the bond valence site energy theory is induced to reveal the possible lithium-ion migration channel. The results show that modification with LiF enhanced the 3D migration pathways and conductivity of LZNO-based electrolytes. The 5 wt% LiF modified LZNO presents total conductivity of 0.943 × 10 −4 S cm −1 at ambient temperature and has low activation energy of conduction (0.16 eV). The cycle performance of the lithium symmetric cell characterizes the cycle of 140 h.
A series of novel low-permittivity microwave dielectric ceramics with the compositions of (1- x ) BaY 2 Si 3 O 10 - x Ba 5 Si 8 O 21 (0.3 ≤ x ≤ 0.7) and 0.4 BaY 2 Si 3 O 10 -0.6 Ba 5 Si 8 O 21 - y wt% LiF (1 ≤ y ≤ 3) were successfully synthesized using solid-state reaction sintering. The phase evolution and microwave dielectric properties of these ceramics were systematically studied. X-ray diffraction analysis indicated the coexistence of BaY 2 Si 3 O 10 and Ba 5 Si 8 O 21 phases in the (1- x ) BaY 2 Si 3 O 10 - x Ba 5 Si 8 O 21 system, with no secondary phases detected. In contrast, an additional Ba 2 Si 3 O 8 phase was identified in the LiF-modified composition (0.4 BaY 2 Si 3 O 10 -0.6 Ba 5 Si 8 O 21 - y wt% LiF (1 ≤ y ≤ 3)). Moreover, the Ba 5 Si 8 O 21 phase was found to effectively tune the temperature coefficient of resonant frequency (τ f ) to near-zero values in both systems. Excellent microwave dielectric properties were obtained for the 0.4 BaY 2 Si 3 O 10 -0.6 Ba 5 Si 8 O 21 - 2 wt% LiF ceramic, exhibiting a permittivity ( ε r ) of 7.45, a quality factor ( Q × f ) of 13,152 GHz, and a τ f value of −3.17 ppm/°C. This composition also showed good chemical compatibility with silver electrodes, suggesting its potential for use in low-temperature co-fired ceramic (LTCC) applications.
High-voltage LiCoO 2 (LCO) can deliver a high capacity and therefore significantly boost the energy density of Li-ion batteries (LIBs). However, its cyclability is still a major problem in terms of commercial applications. Herein, we propose a simple but effective method to greatly improve the high-voltage cyclability of an LCO cathode by constructing a surface LiF modification layer via pyrolysis of the lithiated polyvinylidene fluoride (Li-PVDF) coating under air atmosphere. Benefitting from the good film-forming and strong adhesion ability of Li-PVDF, the thus-obtained LiF layer is uniform, dense, and conformal; therefore, it is capable of acting as a barrier layer to effectively protect the LCO surface from direct exposure to the electrolyte, thus suppressing the interfacial side reactions and surface structure deterioration. Consequently, the high-voltage stability of the LCO electrode is significantly enhanced. Under a high charge cutoff voltage of 4.6 V, the LiF-modified LCO (LiF@LCO) cathode demonstrates a high capacity of 201 mA h g −1 at 0.1 C and a stable cycling performance at 0.5 C with 80.5% capacity retention after 700 cycles, outperforming the vast majority of high-voltage LCO cathodes reported so far.
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