《厦门大学学报（自然科学版）》

通过射频磁控溅射制备Li1.3Al0.3Ti1.7(PO4)3(LATP)薄膜.X-射线衍射表征表明沉积的LATP薄膜为非晶态.改变溅射功率和氩气气压,发现在较大溅射功率(200 W)和较低气压(0.3 Pa)下制备的LATP薄膜具有较高的锂离子电导率,达到1.16×10-4 S/cm.将该优化条件下制备的LATP薄膜组装成Cu/LiCoO2/LATP/LiCoO2/Cu全固态薄膜对称电池,在7.8 μA/cm2电流密度下循环700 h,极化电压依然稳定.以上结果显示LATP薄膜有望在固态薄膜锂离子电池中得到广泛应用.

Objective: With the rising demand for portable devices such as electronic chips, smart cards and medical implants, all solid-state thin film batteries have received widespread attention as a power source for micro-devices because of their safety, wide potential window and large capacity. As an excellent solid electrolyte for thin film battery, the Li1+xAlxTi2-x(PO4)3 (LATP) with a NASICON-type structure has been extensively researched because of its comparatively low electronic conductivity and relatively high ionic conductivity. Here we examined how to improve the ionic conductivity of LATP thin films by magnetron sputtering and focused on its performance in the thin-film batteries.
Methods: Ceramic LATP target was prepared with a solid phase method. The LATP thin films were deposited by RF magnetron sputtering method in Ar atmosphere with 80-200 W power and 0.3-1.2 Pa gas pressure for 3 h. The structures of the target and thin films were characterized by X-ray diffraction (XRD). In order to measure the ionic conductivity of LATP thin films, Cu/LATP/Cu sandwiched structure was prepared by mask technique and sputtering method. The Cu electrode was deposited by direct-current magnetron sputtering with a sputtering power of 80 W and a sputtering argon pressure of 0.8 Pa. A thin film symmetric cell with the structure of Cu/LiCoO2/LATP/LiCoO2/Cu was assembled with the sputtered LATP thin film as the electrolyte to verify its charge-discharge performance.
Results: XRD results showed that all the diffraction peaks of the target could be ascribed to the LiTi2(PO4)3 crystal phase. Scanning electron microscope (SEM) images of surfaces morphology and atomic force microscope (AFM) photographs showed that the LATP thin film deposited on Si substrate was composed of fine particles, and was smooth without noticeable cracks or pin holes on the surface. The films had an amorphous structure confirmed by XRD pattern. The electronic conductivity of the films deposited from different conditions was from 1.5×1012 S/cm to 8.6×10-11 S/cm, suggesting excellent electronic insulation property of the films. The ionic conductivity of LATP films was determined by alternating current impedance spectroscopy of the Cu/LATP/Cu sandwiched structure. In this work, the impedance spectroscopy of as-deposited LATP films consisted of only one semi-circle without a tail due to their amorphous structure. Results calculated from the impedance spectra showed that the ionic conductivity of the film increased with the sputtering power, and showed a trend of increasing and then decreasing with the sputtering pressure. It was found that under the condition of high sputtering power (200 W) and low pressure (0.3 Pa), the LATP film achieved an ion conductivity (1.16×10-4 S/cm) much higher than values reported in the literature (up to 2.46×10-5 S/cm). The Ti3+ content and Li+ diffusion activation energy of LATP film prepared at 200 W and 0.3 Pa were both lower than that of LATP film prepared at 200 W and 0.8 Pa. This indicates that low sputtering pressure is beneficial to improve the ionic conductivity of LATP films. Finally, a symmetric thin film battery cell was assembled with the structure of Cu/LiCoO2/LATP/ LiCoO2/Cu. It was found that the LATP film prepared under 200 W and 0.3 Pa sputtering condition was relatively stable during cycling for 700 h at a current density of 7.8 μA/cm2, indicating that LATP is an ideal electrolyte material for the preparation of thin-film Li-ion batteries.
Conclusion: LATP thin film was prepared with RF magnetron sputtering. The deposited LATP films were amorphous based on X-ray diffraction. With the adjustments of sputtering power and argon gas pressure, it was found that when prepared under a higher sputtering power of 200 W and a lower pressure of 0.3 Pa, the LATP film had the highest lithium ion conductivity of 1.16×10-4 S/cm. The LATP thin film prepared under this optimized condition was assembled into a Cu/LiCoO2/LATP/LiCoO2/Cu all-solid-state thin-film symmetric battery. The polarization voltage was observed to be stable during cycling for 700 h at a current density of 7.8 μA/cm2. Overall, our results indicate that the LATP film is expected to be widely used as an electrolyte layer in solid-state thin-film lithium-ion batteries.

引言
1 实验部分
2 结果与讨论
3 结论

图1 LATP靶材的XRD谱图<br/>Fig.1 XRD pattern of the LATP target

图1 LATP靶材的XRD谱图
Fig.1 XRD pattern of the LATP target

图2 不同溅射功率下制备的LATP薄膜表面的SEM图<br/>Fig.2 SEM images of the LATP thin films prepared with various sputtering powers

图2 不同溅射功率下制备的LATP薄膜表面的SEM图
Fig.2 SEM images of the LATP thin films prepared with various sputtering powers

图3 LATP薄膜的EDS元素面扫图<br/>Fig.3 EDS elemental mapping of the LATP thin film

图3 LATP薄膜的EDS元素面扫图
Fig.3 EDS elemental mapping of the LATP thin film

图4 Cu/LATP/Cu三层结构的示意图(a)及其SEM截面图(b),不同溅射功率下制备的LATP薄膜的XRD谱图(c)、阻抗图(d)、离子电导率和沉积速率(e)及直流电流-电压(I-V)曲线(f)<br/>Fig.4 Schematic diagram(a)and SEM cross-section image(b)of the Cu/LATP/Cu three-layer structure,XRD patterns(c), electrochemical impedance spectra(d),ionic conductivities and deposited rates(e),and I-V curves(f)of the LATP thin films prepared with various sputtering powers

图4 Cu/LATP/Cu三层结构的示意图(a)及其SEM截面图(b),不同溅射功率下制备的LATP薄膜的XRD谱图(c)、阻抗图(d)、离子电导率和沉积速率(e)及直流电流-电压(I-V)曲线(f)
Fig.4 Schematic diagram(a)and SEM cross-section image(b)of the Cu/LATP/Cu three-layer structure,XRD patterns(c), electrochemical impedance spectra(d),ionic conductivities and deposited rates(e),and I-V curves(f)of the LATP thin films prepared with various sputtering powers

图5 溅射功率200 W时不同气压下沉积的LATP薄膜的AFM图<br/>Fig.5 AFM images of the LATP thin films sputtered with a power of 200 W and under various gas pressures

图5 溅射功率200 W时不同气压下沉积的LATP薄膜的AFM图
Fig.5 AFM images of the LATP thin films sputtered with a power of 200 W and under various gas pressures

图6 不同溅射气压下制备的LATP薄膜的XRD谱图(a)、阻抗图(b)、离子电导率和沉积速率(c)及I-V曲线(d)<br/>Fig.6 XRD patterns(a),electrochemical impedance spectra(b),ionic conductivities and deposited rates(c), and I-V curves(d)of the LATP thin films prepared under various sputtering powers

图6 不同溅射气压下制备的LATP薄膜的XRD谱图(a)、阻抗图(b)、离子电导率和沉积速率(c)及I-V曲线(d)
Fig.6 XRD patterns(a),electrochemical impedance spectra(b),ionic conductivities and deposited rates(c), and I-V curves(d)of the LATP thin films prepared under various sputtering powers

图7 0.3 Pa(a)和0.8 Pa(b)下沉积的LATP薄膜在不同测试温度下的电化学阻抗谱及其lg(σT)-T-1曲线(c)<br/>Fig.7 Temperature dependent electrochemical impedance spectra of the LATP thin films prepared under 0.3 Pa(a)and 0.8 Pa(b),and their lg(σT)-T-1 curves(c)

图7 0.3 Pa(a)和0.8 Pa(b)下沉积的LATP薄膜在不同测试温度下的电化学阻抗谱及其lg(σT)-T-1曲线(c)
Fig.7 Temperature dependent electrochemical impedance spectra of the LATP thin films prepared under 0.3 Pa(a)and 0.8 Pa(b),and their lg(σT)-T-1 curves(c)

图8 0.3和0.8 Pa下制备的LATP薄膜样品的Ti峰拟合<br/>Fig.8 Ti peak fitting of LATP thin film samples prepared at 0.3 and 0.8 Pa

图8 0.3和0.8 Pa下制备的LATP薄膜样品的Ti峰拟合
Fig.8 Ti peak fitting of LATP thin film samples prepared at 0.3 and 0.8 Pa

图9 SiO2/Cu/LiCoO2/LATP@0.3 Pa/LiCoO2/Cu/Ti/Quartz结构的全固态薄膜对称电池的截面SEM图(a)和截面元素线扫图(b),0.8和0.3 Pa下制备的LATP薄膜组装成对称电池的循环性能(c),及第350次循环的充放电曲线(d)<br/>Fig.9 SEM cross-section image of the SiO2/Cu/LiCoO2/LATP@0.3 Pa/LiCoO2/Cu/Ti/Quartz structure all-solid-state thin film symmetric battery(a)and line scan of cross-section elements(b),galvanostatic cycling performance of the symmetric batteries assembled by the LATP thin films prepared under 0.8 and 0.3 Pa, respectively(c),and charge-discharge curve of the 350th cycle(d)

图9 SiO2/Cu/LiCoO2/LATP@0.3 Pa/LiCoO2/Cu/Ti/Quartz结构的全固态薄膜对称电池的截面SEM图(a)和截面元素线扫图(b),0.8和0.3 Pa下制备的LATP薄膜组装成对称电池的循环性能(c),及第350次循环的充放电曲线(d)
Fig.9 SEM cross-section image of the SiO2/Cu/LiCoO2/LATP@0.3 Pa/LiCoO2/Cu/Ti/Quartz structure all-solid-state thin film symmetric battery(a)and line scan of cross-section elements(b),galvanostatic cycling performance of the symmetric batteries assembled by the LATP thin films prepared under 0.8 and 0.3 Pa, respectively(c),and charge-discharge curve of the 350th cycle(d)

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引言

1 实验部分

2 结果与讨论

3 结论

学报简介

备注

引言

1 实验部分

2 结果与讨论

3 结 论

学报简介

3 结论