MATERIALS TECHNOLOGY
·
2020
·
IF 1.738
Binggong Yan,Shaoning Lin,Lei Kang,Xuan Song,Zhao Tian,Kaiyong Jiang
Laser annealing is used for preparation of LiMn2O4. The electrochemical characterisation shows that the cycle performance of spinel LiMn2O4 is dependent on the power of the laser and the amount of lithium excess. X-ray diffraction is used to study the phase evolution of laser-annealed LiMn2O4. The morphology of LiMn2O4 particles is observed by scanning electron microscope. Electrochemical tests show that the initial capacity of the laser-annealed LiMn2O4 is less than the untreated LiMn2O4, but the cycle performance improved noticeably.
研究领域:
材料科学
·
电化学
✓ 已验证
产品关联
DOI
高影响因子
JOURNAL OF ALLOYS AND COMPOUNDS
·
2024
·
IF 5.8
Huiying Fan,Yun Zhang,Shihua Ding
Li (1+ x ) AlSiO 4 ceramics were synthesized using the conventional solid-state reaction method. X-ray diffraction analysis indicated that they crystallized in single-phase hexagonal structure. Li loss was studied using the thermogravimetric-differential scanning calorimetry (TG-DSC). Appropriate excess Li resulted in sintering temperature reduction from 1325 ℃ to 1225 ℃. The ultra-low dielectric constant ( ε r ) was influenced by the polarizability per unit volume. Theoretical calculations manifested that enhancing the packing fraction suppressed lattice vibrations, resulting in a significant increase in the quality factor ( Q×f ). Compared with the pure phase samples, adding Li ions optimized the thermal stability of the ceramics. Specifically, Li 1.02 AlSiO 4 demonstrated optimal microwave dielectric properties with ε r = 4.13, Q×f = 45,387 GHz and τ f = -35.54 ppm/°C, making it a spacious application prospect in the field of 6 G communication.
研究领域:
材料科学
·
电子工程
✓ 已验证
产品关联
DOI
高影响因子
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS
·
2020
·Vol. 31
·期 16
·13496-13502
·
IF 2.22
Fang Weishuang,Ao Laiyuan,Tang Ying,Li Jie,Xiang Huaicheng,Zhang Zhiwei,Du Qianbiao,Fang Liang
Recently, there have been considerable interests in the Li-containing spinel oxides as promising microwave dielectric materials. Li loss at elevated temperatures, however, is known to be inevitable, resulting in deterioration on dielectric performances. Here the influence of Li nonstoichiometry on the microwave dielectric properties of Li 2 ZnGe 3 O 8 , a spinel oxide, was reported. An appropriate level of Li excess enhanced the densification of Li 2 ZnGe 3 O 8 and increased dielectric performances. In contrast, high level of Li excess induced the formation of the secondary phase of Li 2 ZnGeO 4 confirmed by XRD and Raman spectra, which in turn lowered the dielectric properties. Typically, a composition with x = 0.075, in the Li 2(1+ x ) ZnGe 3 O 8 ceramics exhibited the enhanced microwave dielectric properties with ε r = 10.68, Q × f = 77,300 GHz (at 13.3 GHz), and τ f = − 70.35 ppm/°C when sintered at 940 °C for 4 h. Moreover, these compounds have well chemical compatibility with the silver electrodes.
研究领域:
材料科学
·
陶瓷学
·
电子材料
✓ 已验证
DOI
高影响因子
JOURNAL OF ELECTRONIC MATERIALS
·
2017
·Vol. 46
·期 7
·4047-4051
·
IF 1.579
Li Chunchun,Luo Hao,Xiang Huaicheng,Tang Ying,Fang Liang
A series of low-firing Li 4(1+ x ) WO 5 ( x = 0.02, 0.04, 0.06, 0.08) ceramics were prepared using the solid-state reaction method. Effects of excess lithium on the crystal structure, sintering behavior, and microwave dielectric properties were studied. For x < 0.06 samples, only a single Li 4 WO 5 phase was formed, while a secondary phase detected as Li 6 WO 6 appeared in the x = 0.08 sample. The relative density increased obviously with increasing amount of excess lithium, resulting in the remarkable increase in quality factor. The sample with x = 0.04 sintered at 950°C obtained a high relative density of ∼95.1% and good microwave dielectric properties with ε
r
∼ 9.5, Q × f ∼ 50200 GHz (at 12.2 GHz), τ
f
∼ −3.2 ppm/°C.
研究领域:
材料科学
·
陶瓷工程
✓ 已验证
DOI
高影响因子
Energy Storage Materials
·
2020
·
IF 16.28
Ke Zhou,Shiyao Zheng,Fucheng Ren,Jue Wu,Haodong Liu,Mingzeng Luo,Xiangsi Liu,Yuxuan Xiang,Chunyang Zhang,Wanli Yang,Lunhua He,Yong Yang
Cation-disordered Li-excess cathodes with oxygen redox reactions are promising candidates for high-energy-density Li ion batteries . Nevertheless, the oxygen redox process that is required for the high capacity often comes with the oxygen loss, which leads to severe capacity degradation and voltage decay. In this work, we have successfully synthesized a series of Li-excess cation-disordered cathodes (Li 1.2 Mn 0.4+x Ti 0.4-x O 2-x F x ) (0 ≤ x ≤ 0.2) with different fluorine (F) contents. The electrochemical performance results show that the Li 1.2 Mn 0.55 Ti 0.25 O 1.85 F 0.15 (LMTOF0.15) exhibits the highest reversible capacity (275 mAh g -1 , under 30 mA g -1 ), cyclability, and voltage retentions. The mapping of resonant inelastic X-ray scattering (mRIXS) and differential electrochemical mass spectroscopy (DEMS) results reveal that the fluorination enhances the reversible lattice oxygen redox reaction while suppressing irreversible gas release and surface reactions. The X-ray Absorption Spectroscopy (XAS) during the initial two cycles shows that F-substitution alleviates the reduction of the Mn valence state during the whole (dis)charge processes in the bulk and at the surface of the material, results in higher average discharge voltage. In addition, the introduction of F improves the structural stability and suppresses local lattice distortion of the material. Therefore, LMTOF0.15 is able to cycle with smaller polarization, less interfacial side reaction and Mn dissolution, and therefore results in enhanced cyclability. This work provides a comprehensive understanding of the fluorination effect on the cationic and anionic redox activities in cation-disordered Li-excess cathodes.
研究领域:
材料科学
·
电化学
·
能源存储
✓ 已验证
DOI
高影响因子
RSC Advances
·
2024
·Vol. 14
·期 30
·21799-21807
·
IF 3.9
Yijin Sheng,Fangxu Hu,Yu Wu,De Li,Wenting Ji,Yong Chen
The electrochemical oscillation in Li-ion batteries has been reported for two-phase electrode materials of Li4Ti5O12 and LiCrTiO4, which is originated from the group-by-group phase transition in a multi-particle electrode. For both Li4Ti5O12 and LiCrTiO4, the electrochemical oscillation exhibits usually during charging, while rarely for discharging. Herein, a series of Zr-modified Li4Ti5O12 samples are prepared by using the spray-drying combined with high-temperature sintering method, and the electrochemical oscillation is observed during not only the charging process, but also the discharging process, which gradually grows up and then disappears by increasing the Li content. Compared with Li4Ti5O12, the specific capacity of Zr-modified Li4Ti5O12 decreases gradually by increasing the Zr/Ti ratio, owing to the impurity phases. According to the XRD, XPS and STEM results, the Zr element tends to accumulate on the surface to form ZrO2 nanoparticles, rather than dope into the bulk phase of Li4Ti5O12, which makes Li4Ti5O12 particles well dispersive. In contrast to the Li deficiency for only charging, the electrochemical oscillation during both charging and discharging should be attributed to the Li excess, but too much Li2TiO3 phase will suppress the electrochemical oscillation. Therefore, the Li excess can induce the electrochemical oscillation during both charging and discharging of Zr-modified Li4Ti5O12, which can be adopted to investigate the electrochemical oscillation of other materials in LIBs.
研究领域:
材料科学
·
电化学
·
电池技术
·
纳米技术
✓ 已验证
DOI
高影响因子
JOURNAL OF ALLOYS AND COMPOUNDS
·
2024
·
IF 5.8
Kui Liu,Dainan Zhang,YiDa Lei,Yanlin Ma,Yuran Yang,Cheng Liu,Jie Li,Fang Xu,Huaiwu Zhang
Herein, the feasibility was assessed through first principles, and the effect of lithium excess on both the structure and dielectric properties of Li (1+ x )2 Mg 2 TiO 5 (0.000 ≤ x ≤ 0.200) ceramics was investigated by solid-phase reaction method. An appropriate excess of lithium can moderately inhibit the volatilization of lithium and reduce the production of the secondary phase MgTi 2 O 4 , though it cannot completely inhibit its production. Li (1+0.050)2 Mg 2 TiO 5 exhibits the best dielectric properties with ε r =14.55, Q × f =127,393 GHz (@9.6 GHz), and τ f = −19.91 ppm/°C. The influence of non-inherent factors on the dielectric properties is dominant, with the increase in relative density to 93.53 % and the growth in average grain size to 28.67 μm contributing to the reduction of dielectric loss. The decrease in ε r is due to the decrease in secondary phase content. Results from bond ionicity and Raman wavenumber variations in the intrinsic factors show that the intrinsic factors have little effect on the ε r . Whereas, the increase in lattice energy as well as the decrease in FWHM contribute to the decrease in dielectric loss. In addition, a proper excess of lithium helps to increase the bonding energy thereby optimizing the temperature stability. The optimized Li (1+0.050)2 Mg 2 TiO 5 has great potential for application in microwave communications.
研究领域:
材料科学
·
电气工程
·
陶瓷
✓ 已验证
DOI
高影响因子
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