Al and Ta co-doped LLZO as active filler with enhanced Li⁺ conductivity for PVDF-HFP composite solid-state electrolyte

Abstract

Battery safety calls for solid state batteries and how to prepare solid electrolytes with excellent performance are of significant importance. In this study, hybrid solid electrolytes combined with organic PVDF-HFP and inorganic active fillers are studied. The modified active fillers of Li7-x-3yAlyLa3Zr2-xTaxO12 are obtained by co-element doping with Al and Ta when LLZO is synthesized by calcination. And an high room temperature ionic conductivity of 5.357×10-4 S/cm is exhibited by ATLLZO ceramic sheet. The composite solid electrolyte PVDF-HFP/LiTFSI/ATLLZO (PHL-ATLLZO) is prepared by solution casting method, and its electrochemical properties are investigated. The results show that when the contents of lithium salt LiTFSI and active filler ATLLZO are controlled at 40 wt% and 10%, respectively, the ionic conductivity of the resulting composite solid electrolyte is as high as 2.686×10-4 S/cm at room temperature, and a wide electrochemical window of 4.75 V is exhibited. The LiFePO4/PHL-ATLLZO/Li all-solid-state battery assembled based on the composite solid-state electrolyte exhibits excellent cycling stability at room temperature. The cell assembled by casting the composite solid-state electrolyte on the cathode surface shows a discharge specific capacity of 134.3 mAh/g and 96.2% capacity retention after 100 cycles at 0.2C. The prepared composite solid-state electrolyte demonstrates excellent electrochemical performance.

Composite polymer electrolyte based on poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) for solid-state batteries

“…From the change of current with polarization time, the initial current before polarization is 59 μA, and the current is stable at 38 μA. Therefore, the t Li + value of CPE-10 can be easily calculated as 0.60 according to the Bruce Vincent equation, which is much higher than 0.2 for liquid electrolytes [ 44 ] and other PVDF-HFP based polymer electrolytes [ 2 , 14 , 16 , 17 , 27 , 35 , [45] , [46] , [47] , [48] ] ( Table 1 ). This phenomenon could be related to the interaction between LATP ceramic filler and polymer chain, which relaxed the local chain of polymer and promoted the movement of chain segments [ 49 ].…”

“… SPEs Electrode Ionic conductivity σ (S/cm) Li + transference number ( t Li+ ) Electrochemical window （V） Ref. ATLLZO/PVDF-HFP LiFePO 4 (2.6–4.2 V) 5.35 × 10 −4 (60 °C) 0.37 0.475 [ 2 ] LLZT/PVDF-HFP/IL LiFePO 4 (3.0–3.8 V) 7.63 × 10 −4 (100 °C) 0.61 5.3 [ 14 ] LATP/PVDF-HFP LiFePO 4 (2.5–4.0 V) 2.3 × 10 −4 (60 °C) – – [ 16 ] LATP/PEG PVDF-HFP LiFePO 4 (2.5–3.6 V) 8.13 × 10 −4 (40 °C) 0.58 – [ 17 ] LLSZO/PVDF-HFP/LiPF6 – 2.94 × 10 −3 (35 °C) 4.5 – [ 27 ] NMP-LE/PVDF-HFP LiFePO 4 (2.5–3.8 V) 7.24 × 10 −4 (70 °C) 0.57 5.2 [ 35 ] LLZO/PVDF-HFP LiFePO 4 (2.4–4.0) 3.71 × 10 −4 (30 °C) 0.58 4.65 [ 45 ] Lithium magnesium silicate/PVDF-HFP NCM622 (2.8–4.3 V) ...…”

“…Developing clean and efficient energy storage equipment is an effective strategy to solve the increasingly serious energy crisis and environmental pollution problems. Among various energy storage devices, lithium-ion batteries have become one of the most popular ones due to their large size and high energy density [ [1] , [2] , [3] ]. At present, the energy density of lithium-ion batteries based on intercalated materials is not only difficult to meet the requirements of long-distance transportation, but flammable liquid electrolytes also pose potential safety issues for batteries, especially in the application of large batteries in electric vehicles and power grids [ 4 , 5 ].…”

Elucidating the Importance of Quaternary Dopants in Stabilizing Cubic LLZO at Low Temperature

“…For the stabilization of cubic LLZO, researchers adopted the incorporation of dopants (impurities) at certain sites (Li/La/Zr) of the crystal, where the dopants act as sintering aids to enhance the densification, in turn stabilizing cubic LLZO . Also, doping serves to maintain charge neutrality by creating Li vacancies and increase disorder within the framework, thereby enhancing the stabilization of a cubic phase with high ionic conductivity . However, stabilization of cubic LLZO at low calcination temperatures is still a big challenge …”

“…7 Also, doping serves to maintain charge neutrality by creating Li vacancies and increase disorder within the framework, thereby enhancing the stabilization of a cubic phase with high ionic conductivity. 8 However, stabilization of cubic LLZO at low calcination temperatures is still a big challenge. 9 To overcome the aforementioned challenges, this work utilizes a quaternary doping strategy by substituting Ga and Mg dopants at Li sites and Ta and Nb dopants at Zr sites, to achieve cubic LLZO at low temperature (800 °C) using a solid-state approach.…”