## 4 Materials and Methods
### Electrochemical Testing  
Ionic conductivity can reflect whether polymer gel electrolytes can meet the standards of solid-state batteries. A coin cell symmetric configuration (stainless steel (SS)/CSE/SS) was assembled and tested on an electrochemical workstation (DH 7000, Jiangsu, China) using electrochemical impedance spectroscopy (EIS) in the frequency range of 0.1 Hz to 1 MHz with an amplitude of 10 mV. The ionic conductivity (\(\sigma\)) can be calculated using the following equation:  
\[\sigma=\frac{L}{RS}. \tag{1}\]  
In this equation, \(L\) denotes the electrolyte membrane thickness (cm), \(R\) is the bulk resistance (\(\Omega\)) obtained from EIS fitting, and \(S\) represents the effective contact area (cm\({}^{2}\)) between the electrode and the electrolyte membrane.  
The lithium-ion transference number (\(t_{Li}\)\({}^{+}\)) is a key parameter for evaluating the contribution of lithium ions to the total ionic conductivity of the electrolyte and serves as an important criterion for determining the performance of lithium-ion batteries. The \(t_{Li}\)\({}^{+}\) of the composite gel electrolyte (CGE) is measured using a symmetric cell (Li/CGE/Li) by combining electrochemical impedance spectroscopy (EIS) and direct current (DC) polarization on an electrochemical workstation. First, the initial impedance value (\(R_{0}\)) is obtained through EIS testing. A small DC voltage is then applied, and the current is allowed to reach a steady-state value (\(Is\)). After removing the DC voltage, the impedance spectrum is measured again to obtain the interfacial resistance after polarization (\(R_{s}\)).  
The lithium-ion transference number (\(t_{Li}\)\({}^{+}\)) is calculated using the following equation:  
\[t_{Li}\)\({}^{+}=\frac{I_{s}(\Delta V-R_{0}I_{0})}{I_{0}(\Delta V-R_{s}I_{S})}. \tag{2}\]  
In Equation (2), \(R_{0}\) and \(R_{s}\) represent the impedance values before and after DC polarization, respectively; \(\Delta V\) is the applied voltage across the battery (10 mV); and \(I_{0}\) and \(I_{s}\) denote the initial and steady-state currents, respectively [40].  
To assess the electrochemical stability range of the CGE, a Li/CGE/WE cell was built and subjected to linear sweep voltammetry (LSV) over a voltage span of 2.0-6.0 V (vs. Li/Li\({}^{+}\)) at a scan rate of 0.5 mV/s.  
The rate performance and cycling stability of the battery were evaluated using a battery testing system (Newware, Dongguan, China). Coin cells were assembled with LiFePO\({}_{4}\) as the cathode and lithium metal as the anode, and their cycling and rate performance were measured. The tests were conducted within a voltage range of 2.8-4.0 V.  
Conceptualization, N.M. and X.L.; methodology, Q.H.; software, L.L.; validation, X.L., N.M. and Q.H.; formal analysis, N.M.; investigation, J.W.; resources, X.L.; data curation, N.M.; writing--original draft preparation, N.M.; writing--review and editing, X.L.; visualization, L.L. and Y.G.; supervision, L.L. and Y.G.; project administration, J.W.; funding acquisition, L.L. and Y.G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Reginal Collaboration R&D Program of Sichuan Province under Grant (No. 2024 YFHIZ0209), the Fund Project of the Guangxi Key R&D Programme Projects (No. AB24010346), the National Natural Science Foundation of China (Nos. 22462003, 52161033, and 22262005), the Guangxi Key Laboratory of Automobile Components and Vehicle technology (Nos. 2023 GKLACVTZZ02, 2022 GKLACVTZZ04, 2023 GKLACVTZZ10), ), and the Guangxi University Young and Middle-Agged Teachers' Basic Scientific Research Ability Improvement Project (No. 2021 KY1715).  
Not applicable.  
The data are contained within the article.  
The authors declare no conflicts of interest.