The influences of multifactors in the synthesis progress on the characteristics of lithium lanthanum zirconate solid electrolytes

doi:10.19799/j.cnki.2095-4239.2022.0646

Abstract

Abstract:

Lithium lanthanum zirconate (Li₇La₃Zr₂O₁₂, LLZO) solid-state electrolytes were synthesized using the chemical coprecipitation method. The effects of the operation parameters of the sintering process, ball milling, Al doping, and compression force on the grain boundary, phase, densification, and final Li⁺ ion conductivity were evaluated using various characterization techniques, e.g., scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS) analyses. Wet ball milling using isopropanol as a grinding aid or hot-pressed sintering is beneficial for improving the density of LLZO pellets. However, the Li⁺ ion conductivities at room temperature of the samples is low due to their poor structures. The cubic phase structure (c-LLZO) was synthesized via dry ball milling and pressure less sintering, and the crystal structures became pure as the sintering temperature increased. To solve the subsequent problem of the grain coarsening, a two-step sintering was proposed instead of one-step sintering to synthesize LLZO electrolytes with small particle sizes and high relative density. At the same time, the effect of Al doping in stabilizing the cubic structure was also enhanced using the two-step sintering. Finally, the as-prepared Al-doped LLZO solid-state electrolyte obtained via dry ball milling, cold pressing at 750 MPa, and two-step sintering of 1100 ℃ for 6 h and 1200 ℃ for 20 h exhibited the highest ionic conductivity (1.52×10^-4 S/cm), mainly owing to its cubic garnet structure and the highest relative density. This research will shed light on preparing and applying LLZO-related ceramic materials, providing a solid basis and guidance for developing solid-state battery technology.

Key words: solid-state electrolytes, chemical co-precipitation, high-temperature sintering, Al doping, ball milling

CLC Number:

TM 911.3

Lei LEI, Peng GAO, Nana FENG, Kunpeng CAI, Hai ZHANG, Yang ZHANG. The influences of multifactors in the synthesis progress on the characteristics of lithium lanthanum zirconate solid electrolytes[J]. Energy Storage Science and Technology, 2023, 12(5): 1625-1635.

Figures/Tables 9

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Table 1

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Table 2

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样品名称	球磨方式	铝掺杂	压片压力/MPa	烧结温度/℃、时长/h(压力/MPa)
LLZO-1150	干法	否	250	1150 ℃×20 h
LLZO-1180	干法	否	250	1180 ℃×20 h
LLZO-1200	干法	否	250	1200 ℃×20 h
LLZO-1200-HP	干法	否	250	1200 ℃×20 h-1200 ℃×2 h(40 MPa)
Wet-LLZO-1150	湿法	否	250	1150 ℃×20 h
Wet-LLZO-1180	湿法	否	250	1180 ℃×20 h
Wet-LLZO-1200	湿法	否	250	1200 ℃×20 h
LLZAO-1150	干法	是	250	1150 ℃×20 h
LLZAO-1180	干法	是	250	1180 ℃×20 h
LLZAO-1200	干法	是	250	1200 ℃×20 h
LLZAO-1100/1200-250	干法	是	250	1100 ℃×6 h-1200 ℃×20 h
LLZAO-1100/1200-500	干法	是	500	1100 ℃×6 h-1200 ℃×20 h
LLZAO-1100/1200-750	干法	是	750	1100 ℃×6 h-1200 ℃×20 h

样品	颗粒尺寸/μm	相对密度/%	离子电导率/(S/cm)	数据来源
LLZO-1150	10	81.1	1.23×10^-5	本工作
LLZO-1180	12.5	82.7	1.26×10^-5	本工作
LLZO-1200	17.5	82.7	1.42×10^-5	本工作
LLZO-1200-HP	—	97.7	6.66×10^-6	本工作
Wet-LLZO-1150	20	89.6	7.69×10^-6	本工作
Wet-LLZO-1180	26	90.0	9.95×10^-6	本工作
Wet-LLZO-1200	40	92.4	1.06×10^-5	本工作
LLZAO-1150	10	81.5	2.28×10^-5	本工作
LLZAO-1180	14	80.4	1.82×10^-5	本工作
LLZAO-1200	16	83.3	1.82×10^-5	本工作
LLZAO-1100/1200-250	10	92.7	8.82×10^-5	本工作
LLZAO-1100/1200-500	10	92.9	9.37×10^-5	本工作
LLZAO-1100/1200-750	10	93.1	1.52×10^-4	本工作(最佳样品)
LLZO	略大于10	略大于90	2×10^-4	参考文献[13]
Al-LLZO	6.23	86.8	2.02×10^-4	参考文献[8]
Al-LLZO	10	80	2.8×10^-6	参考文献[15]
Al-LLZO	5	57	6.3×10^-5	参考文献[3]
Ta-LLZO	15	92	6.9×10^-4	参考文献[5]
Ti-LLZO	8	90.7	1.91×10^-4	参考文献[7]

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