Gradual gradient distribution composite solid electrolyte for solid-state lithium metal batteries with ameliorated electrochemical performance

Li6.4La3Zr1.4Ta0.6O12 (LLZTO) exhibited a gradual gradient distribution from the center to the periphery in PEO, demonstrating exceptional electrochemical properties and representing a promising high-performance material for all-solid-state lithium metal batteries. [Display omitted] •GCSE with LLZTO gradient descending from center to edge were prepared.•There is no distinct macroscopic interface between GCSE layers with high ionic conductivity.•The cycle stability time of Li|GCSE|Li exceeds 1200 h.•LiFePO4|GCSE|Li battery enable high energy density and cycling stability. Composite solid electrolytes (CSEs) have emerged as promising contenders for tackling the safety concerns associated with lithium metal batteries and attaining elevated energy densities. Nonetheless, augmenting ion conductivity and curtailing the growth of lithium dendrites within the electrolyte remain pressing challenges. We have developed CSEs featuring a unique structure, in which Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is distributed in a gradient decline from the center to both sides (GCSE). This distinctive arrangement encompasses heightened polymer content at the edges, thereby enhancing the compatibility between CSEs and electrode materials. Concurrently, the escalated LLZTO content at the center functions to impede the proliferation of lithium dendrites. The uniform gradient distribution state facilitates the consistent and rapid transport of lithium ions. At room temperature, GCSE exhibits an ionic conductivity of 1.5 × 10−4 S cm−1, with stable constant current cycling of lithium for over 1200 h. Furthermore, CR2032 coin batteries with a LiFePO4 (LFP)|GCSE|Li configuration demonstrate excellent rate performance and cycling stability, yielding a discharge capacity of 120 mA h g−1 at 0.5C and retaining 90 % capacity after 200 cycles at 60 °C. Flexible solid electrolytes with gradient structures offer substantial advantages in dealing with ion conductivity and inhibition of lithium dendrites, thereby expected to propel the practical application of lithium metal batteries.