A dual-locked anions strategy constructing a composite electrolyte film for stable solid-state lithium metal batteries

The practical application of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based composite solid-state electrolytes (CSEs) incorporating garnet-type Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) is hindered by poor organic-inorganic interfacial compatibility. Residual Li 2 CO 3 /LiOH on LLZTO causes filler agglomeration and interfacial polarization. Herein, we propose an interfacial engineering strategy using a brief (10 s) dilute hydrochloric acid pickling treatment to remove alkali impurities from LLZTO without damaging its structure. The modified LLZTO surface, with exposed Lewis acid sites and trace Li 2 CO 3 , induces controlled dehydrofluorination of PVDF-HFP, generating −C=C− bonds along polymer chains. This creates a “dual-locked anions” mechanism that firmly anchors TFSI − anions. The optimized PVDF-HFP/LLZTO CSE achieves a high ionic conductivity of ∼1 mS cm −1 at room temperature and a lithium-ion transference number of 0.47, effectively suppressing lithium dendrite growth and interfacial polarization. The assembled solid-state lithium metal battery using LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode exhibits exceptional cycling stability (138.42 mAh g −1 after 200 cycles between 2.8 V and 4.3 V), high Coulombic efficiency (>99% even between 2.8 and 4.5 V), and a broad operating temperature range (from −20 °C to 80 °C). This work offers a novel strategy for high-performance CSEs through interfacial anion dynamics management.