Solid electrolytes are safer alternatives to liquid electrolytes. Adding Ga to lithium lanthanum zirconium oxide (LLZO) garnet-like solid-state electrolytes effectively improves their performance. The properties of solid-state electrolytes prepared using the two mainstream methods, namely, electrospinning and sol-gel, vary and directly affect the electrochemical performance of assembled batteries. In this study, we prepared Li 6.25 Ga 0.25 La 3 Zr 2 O 12 (Ga-LLZO) nanoparticles and nanofibers using the sol-gel and electrospinning methods, respectively. The battery was also assembled with composite film consisting of the poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer substrate within Ga-LLZO ceramic fillers. The electrolyte of the battery prepared by Ga-LLZO nanofibers has better conductivity. We fabricated a Li|10 wt% Ga-LLZO nanofiber/PVDF-HFP/60 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)|LiFePO 4 button battery using the optimal concentration. The device demonstrated a stable cycle lasting up to 700 h, a Coulombic efficiency of 98%, a capacity retention rate of 96.5%, and an electrochemical window up to 5 V vs Li/Li + at room temperature. Over time, a suitable contact interface generated a positive feedback loop. The ionic conductivity was 1.1 × 10 −4 S·cm −1 . The newly prepared electrolyte films aid the fabrication of future solid electrolytes.
Yao Lu,Xiaoyi Meng,José A. Alonso,María T. Fernández-Díaz,Chunwen Sun
Solid-state lithium batteries (SSLBs) are promising technologies with great potential in improving safety and energy density, compared with the traditional liquid based lithium ion batteries. However, the bottleneck of SSLBs lies in the issues of poor interface contact and low electrolyte conductivity. In this work, the crystal structure of garnet-type Li6.25Ga0.25La3Zr2O12 (LGLZO) was engineered more rigidly with subdued atoms displacement by fluorine doping and thus smoother and faster lithium ion diffusion paths are formed. The ionic conductivity of garnet-type electrolyte is significantly increased from 5.43 × 10–4 S/cm to 1.28 × 10–3 S/cm at 25 °C and the activation energy is reduced from 0.33 to 0.28 eV. The solid-state symmetric cell consisting of F doped Li6.25Ga0.25La3Zr2O12 electrolyte and lithium metal has lower resistance and displays stable lithium plating/stripping for over 650 h with smaller overpotentials than those on LGLZO electrolyte. Moreover, the all solid-state lithium battery with F-LGLZO electrolyte and LiFePO4 composite electrode exhibits an improved rate capability, which can still keep 132.9 mAh/g at 1 C. Fluorine substitution in garnet-type electrolyte opens new avenues to design new solid-state electrolytes for practical applications of SSLBs.
Solid-state lithium metal batteries (LMBs) using nonflammable solid electrolytes (SEs) are considered to be the new generation of energy storage devices with high energy density and good safety. However, many challenges, such as insufficient room-temperature ionic conductivity of SEs and tremendous electrode-electrolyte interfacial impedance, hinder the commercialization of solid-state LMBs. Here, we reported a novel composite solid electrolyte (CSE), consisting of a three-dimensional (3D) Li 6.25 Ga 0.25 La 3 Zr 2 O 12 (LLZO) nanoparticle-based framework and filled tripropylene gycol diacrylate (TPGDA)-based gel electrolytes, in which the gel electrolytes are prepared by in situ polymerization of the TPGDA monomer in the condition of liquid electrolyte . Owing to the high content of LLZO powder and PVDF binder, the nonflammable CSE shows superior thermal stability and outstanding mechanical property. Moreover, the CSE exhibits high room-temperature ionic conductivity (1.66 × 10 −3 S⋅cm −1 ) due to the large amount of liquid electrolyte loaded in the 3D framework. Besides, in-situ gel electrolytes facilitate the interfacial contact between electrolyte and lithium anode. Therefore, the LiFePO 4 /CSE/Li cell exhibits excellent cycling stability at room temperature , delivering a capacity retention ratio of 86.5% after 350 cycles at 1 C. This work can provide guidance in designing CSEs for high-performance lithium metal batteries.
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