Muhammad Waqas,Shamshad Ali,Dongjiang Chen,Bismark Boateng,Yupei Han,Mei Zhang,Jiecai Han,John B. Goodenough,Weidong He
Poly(vinylidene fluoride-hexafluoropropylene)-lanthanum oxide // poly(vinylidene fluoride-hexafluoropropylene)-hexagonal boron nitride (PVH–LaO // PVH-BN) bi-layer separators are developed through a two-step blading approach. La 2 O 3 in the PVH matrix enhances the Li + conduction by providing extra Li + conducting pathways owing to the Lewis acid-base interaction of La atoms with the PVH chains, leading to a high lithium-ion transference number of 0.72 and ionic conductivity of 7.5 × 10 −4 S cm −1 at room temperature. Moreover, the strong interfacial interaction between h -BN and PVH in the bi-layer separator enhances the thermal and mechanical stabilities of the separator. Batteries based on lithium iron phosphate and the bi-layer separator deliver a discharge capacity of 158 mAh g −1 at 0.5 C after 100 cycles and a rate capacity of 81 mAh g −1 at 10 C after 1500 cycles.
Composite solid electrolytes (CSEs) integrate the fast ion conductivity of inorganic electrolytes and the excellent interfacial compatibility of polymer electrolytes. Typically, fluoropolymers and garnets are promising individuals to formulate cutting-edge CSEs owing to their unique properties. However, the alkaline garnets can induce the dehydrofluorination of fluoropolymers, deteriorating their CSEs performance. Here, for the first time, NH 4 HCO 3 is proposed as a sacrificial inhibitor to effectively prevent the garnet-induced dehydrofluorination, using Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) and poly(vinylidene fluoride- co -hexafluoropropylene) (PVH) as symbolic garnets and fluoropolymers, respectively. Various findings demonstrate that NH 4 HCO 3 can buffer the alkalinity of LLZTO, thereby inhibiting the dehydrofluorination of PVH. In addition, NH 4 HCO 3 can completely decompose to volatiles upon drying without compromising the properties of LLZTO and PVH. Additionally, a polymer-in-salt strategy is further introduced by adding high-concentration LiTFSI salt to the above system, resulting in the PVH/LiTFSI/LLZTO (PLL) CSEs. Benefiting from the synergetic coupling of the sacrificial inhibitor and polymer-in-salt strategies, the PLL exhibits an exceptionally high ionic conductivity of 1.2 mS cm −1 at 25 °C and stable voltage of 5.09 V, outperforming other reported CSEs. Consequently, the PLL delivers impressive high-rate cyclability in solid-state lithium-metal batteries with an outstanding capacity retention of 95.4% after 240 cycles at 1 C (25 °C).
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