Preparation and performances of gelatin/polyethylene oxide composite electrolyte for high-voltage solid-state lithium batteries
ZHENG Yansen,, WANG Yongyin,, GUI Jiuqing, XIE Zhuohao, XU Yue, CAO Qiaoying,, XU Yuehua,, LIU Yingliang, LIANG Yeru,
Key Laboratory for Biobased Materials and Energy of Ministry of Education, College of Materials and Energy, South China Agricultural University, Guangzhou 510642, Guangdong, China
The unstable interface of polyethylene oxide (PEO)-based electrolytes at high voltage seriously hinders their practical application in high-energy density solid-state lithium batteries.This study presents a new approach of constructing high-voltage solid-state lithium batteries based on the PEO/gelatin composite electrolyte. The results indicate that the oxidative decomposition of the hydroxyl groups at the end of the PEO-based electrolyte chain mainly causes the voltage noise behavior of the Li | PEO | NCM811 at voltages greater than 4.0 V. To address this issue, the gelatin carboxyl group is utilized to form hydrogen bonds with the hydroxyl end groups of the PEO chain, slowing down the PEO hydroxyl group oxidation under a high voltage. The hydroxyl terminal oxidation side reaction of the PEO/gelatin composite electrolyte is suppressed at 4.0—4.3 V after gelatin addition. The results show that adding macromolecular gelatin reduces the PEO crystallinity and forms a fast Li ion conductor pathway that improves the ion conductivity of the composite electrolyte, which consequently improves the high-voltage stability of the matched high-voltage cathode, NCM811. This work presents a simple approach of constructing PEO-based polymer electrolytes for high-voltage solid-state lithium batteries.
Keywords：solid-state lithium batteries
;
polyethylene oxide
;
composite electrolyte
;
gelatin
;
high voltage
;
interface stability
ZHENG Yansen. Preparation and performances of gelatin/polyethylene oxide composite electrolyte for high-voltage solid-state lithium batteries[J]. Energy Storage Science and Technology, 2023, 12(10): 3064-3074
Fig. 1
(a) Schematic diagram of the preparation process of G/PEO electrolyte; (b) SEM and EDS elemental images of G/PEO electrolyte; (c) Optical digital photos show the flexibility of G/PEO; (d) XRD patterns of PEO, PEO electrolyte, and G/PEO electrolyte; (e) FTIR spectrum of PEO and G/PEO electrolyte
Fig. 2
(a) Electrochemical impedance spectroscopy and (b) ion conductivity of PEO and G/PEO electrolytes at 60 ℃; The activation energies of (c) G/PEO and (d) PEO were calculated using the Arrhenius equation at 25—80 ℃; (e) Activation energy and (f) LSV Curve of PEO and G/PEO
PEO和G/PEO电解质在不同温度下的离子电导率如图2(c)、(d)所示，随着温度的提升，两种电解质的离子电导率相应提升。值得注意的是，在不同温度下G/PEO复合电解质的离子电导率均高于传统PEO电解质。通过对不同温度下的离子电导率进行线性拟合，结合Arrhenius公式算出离子跃迁活化能。随着明胶的引入，复合电解质的离子跃迁活化能(Ea)相比于传统PEO电解质从0.63 eV降至0.43 eV [图2(e)]，有利于锂离子在聚合物链中的跃迁。为了解复合电解质的电化学窗口及耐压性能，采用线性扫描伏安法(LSV)进行表征，PEO和G/PEO电解质的LSV测试结果如图2(f)所示。相比于PEO电解质的低电化学稳定窗口(4.0 V左右)，G/PEO电解质的电化学稳定窗口由4.0 V扩展到4.8 V，可能是明胶与PEO链之间的相互作用使复合电解质具备更宽的耐压窗口。具有4.5 V以上的高分解电压是G/PEO复合固态电解质能较好兼容匹配高压正极材料的前提条件，有效提升了固态锂电池的能量密度。
Fig. 3
(a) Li | G/PEO|LFP batteries at 3.0—4.2 V and 2.5—4.2 V; (b) Li|PEO|LFP and Li|G/PEO|LFP batteries at 2.5—4.2 V; (c) Li|PEO|NCM811 and Li | G/PEO|NCM811 batteries at 3.0—4.3 V; (d) Voltage distribution diagram of Li|PEO|LFP and (e) Li|G/PEO|LFP at a current density of 0.1 C
Fig. 4
(a) High voltage floating test of G/PEO and PEO at 3.8—4.4 V; (b) The EIS changes of SS|G/PEO|Li and (c) SS|PEO|Li batteries at different times under 4.6 V bias at 60 ℃; (d) FTIR spectra of PEO and G/PEO; (e) ESP surface electrostatic potentials of PEO, glycine, proline, hydroxyproline, and alanine (red and blue regions represent negative and positive charges, respectively)
Fig. 6
(a)—(c) XPS spectra of positive electrode interface components C1s after high voltage storage for 15 hours for Li|PEO|NCM811 and (d)—(e) Li|G/PEO|NCM811
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