Preparation of Lithium Titanate Thin Film for Electrochromic Smart Window by Sol-Gel Spin Coating Method

doi:10.15541/jim20200584

Abstract

Abstract:

Electrochromic materials are attractive for applications like smart windows and thermal management which can modulate transmittance from visible to near-infrared wavelengths. Lithium titanate has been proven to be a potential electrochromic cathode material, but its application prospects in the field of smart windows still lack data support. In this work, Li₄Ti₅O₁₂ thin films with high transmittance and good crystallinity were prepared by Sol-Gel spin coating. The electrochromic properties of the films were characterized by different methods. It is found that all Li₄Ti₅O₁₂ thin films are very sensitive to the test conditions, such as scanning rate, displaying excellent dual band modulation property. Also, the thickness has a significant effect on the initial state transmittance, modulation amplitude, response time, voltage window and cycle durability of the Li₄Ti₅O₁₂ thin films. The colored and bleached response time of the 450 nm Li₄Ti₅O₁₂ is 19.1 and 8.9 s, respectively, while the transmittance modulation is 45% in the visible light region (550 nm). The performance of the films have not been significantly degraded after 20000 s continuous cycle. It is worth mentioning that the transmittance modulation in the near infrared band (1000 nm) is as high as 80%, showing excellent energy saving potential. Finally, Glass/FTO/Li₄Ti₅O₁₂/LiNbO₃/NiO_x/ITO, an all-solid-state inorganic electrochromic device with good cycle performance from gray to blue was successfully assembled. Above data demonstrate that lithium titanate is a strong competitive material for the popularization of electrochromic smart window.

Key words: electrochromic, Li₄Ti₅O₁₂, all-solid-state inorganic device, cycle durability

CLC Number:

TB381

WANG Tianyue, WANG Mengying, HUANG Qingjiao, YANG Jiaming, WANG Shunhua, DIAO Xungang. Preparation of Lithium Titanate Thin Film for Electrochromic Smart Window by Sol-Gel Spin Coating Method[J]. Journal of Inorganic Materials, 2021, 36(5): 471-478.

Figures/Tables 11

Table 1 Preparation parameters of all-solid-state inorganic devices Glass/FTO/Li4Ti5O12/LiNbO3/NiOx/ITO

Target	Power source	Pressure/ Pa	Atmosphere (Ar : O₂)	Power/ W	Time/ min
LiNbO₃	RF	0.8	95 : 5	300	120
Ni	DC	1.5	94 : 6	200	25
ITO	DC	0.3	78.4 : 21.6	200	20

Fig. 1 XRD patterns of Li4Ti5O12 thin films with different thicknesses

Table 2 Lattice constant, interplanar spacing and grain size of Li4Ti5O12 thin films with different thicknesses

Sample	Lattice constant/nm	Interplanar spacing/nm	Average crystallite size/nm
LTO-1	0.834463	0.48055	14.9
LTO-2	0.834586	0.48055	16.2
LTO-3	0.834554	0.48068	15.8
LTO-4	0.834637	0.48055	18.5
LTO-5	0.834687	0.48055	19.4

Fig. 2 SEM surface images (a-e) with insets showing cross-sectional structures and TEM image (f) of Li4Ti5O12 thin films with different thicknesses

Fig. 3 CA curves (a) and in-situ transmittance spectra (b) of Li4Ti5O12 thin films with different thicknesses

Table 3 Transmittance and response time of Li4Ti5O12 thin films with different thicknesses

Sample	T_b/%	T_c/%	ΔT/%	t_c/s	t_b/s
LTO-1	91.84	72.7	19.14	26.3	3.6
LTO-2	90.07	64.35	25.72	20.5	4.5
LTO-3	88.04	37.28	50.76	19.1	8.9
LTO-4	87.4	34.35	53.05	21.8	7.6
LTO-5	75.12	26.19	48.93	28.6	12.0

Fig. 4 CV curves under limited voltage condition (a), in-situ transmittance spectra (b) and CV curves under reasonable voltage condition (c), and in-situ transmittance spectra (d) of LTO-3 at various scan rates

Fig. 5 CV curves (a-e) within 100 cycles and in-situ transmittance spectra (f-j) within 20000 s of Li4Ti5O12 thin films with different thicknesses

Fig. 6 Colored and bleached transmittance spectra of Li4Ti5O12 films with different thicknesses in the wavelength 400-1100 nm

Fig. 7 Schematic diagram of the structure of the all-solid- state inorganic device Glass/FTO/Li4Ti5O12/LiNbO3/NiOx/ITO

Fig. 8 Electrochromic performance of all-solid-state inorganic Glass/FTO/Li4Ti5O12/LiNbO3/NiOx/ITO devices (a) In-situ transmittance spectrum; (b) STEP curves; (c) Transmittance spectrum in the wavelength of 400-1100 nm; (d) Li4Ti5O12 colored and bleached photographs

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