As global energy demand grows exponentially, the heavy use of fossil fuels has contributed significantly to climate change and environmental pollution. The implementation of renewable energy combined with energy storage technologies has become a priority to alleviate oil shortages and solve environmental pollution. Driven by this, an innovative metal battery, called ‘mettery’, manufactured by metal forming technologies was developed. The proposed mettery will enable electrical energy storage in conventional metal components while maintaining the load-bearing capability of the material.
A formable solid-state polyvinylidene fluoride (PVDF)-polymethylhydrosiloxane (PMHS)-Li6.4La3Zr1.4Ta0.6O12 (LLZTO) electrolyte, named PPL electrolyte, was developed as a candidate used in mettery. The PMHS could not only work as a bridge between the PVDF matrix and LLZTO to enhance the mechanical strength but also reduce the desolvation energy of Li-ions from the Li-DMF complex to activate the Li-ion transport pathways through LLZTO. As a result, the PPL electrolyte delivered a high tensile strength of 3.63 MPa and ionic conductivity of 7.5×10-4 S cm-1 at 25 °C, enabling the solid-state NCM811|PPL|Li coin cell to exhibit ultrahigh long-term cycling stability (initial specific capacity of 125.5 mAh g-1 with 81.9% capacity retention after 2200 cycles at 2C).
NCM811|PPL|Li mettery (referred to as PPL-mettery) was manufactured and the effect of plastic deformations on electrochemical performance was studied. The detrimental effect of pure bending deformation on the electrochemical performance was slight when the bending radius-thickness ratio (R/t) was more than 1.77. However, the micro-cracks in tensile deformed PPL electrolyte (tensile strain>10%) hindered the Li-ion transport and caused uneven lithium deposition, leading to an evident negative effect on electrochemical performance. Compared to PPL-mettery (tensile strain of 0.5%), PPL-mettery (tensile strain>10%) showed a capacity decrease of more than 21.7% at 1C and 28.9% at 2C after 100 cycles.
To improve the electrochemical performance of tensile deformed mettery, a small amount of fluoroethylene carbonate (FEC, 5 μL/cm2) was introduced into the PPL electrolyte to form a quasi-solid-state electrolyte (QSE), referred to as PPL+FEC electrolytes. Attributing to the fast ion-conductive network constructed by mobile FEC liquid, the PPL+FEC electrolytes exhibited a high ionic conductivity of 1.5×10-3 S/cm and still maintained 1.3×10-3 S/cm after tensile deformation with a tensile strain of 15% at 25 °C. Moreover, the introduction of FEC helped to construct a stable interface between the electrolyte and lithium metal anode, enhancing the electrochemical performance and limiting the overgrowth of lithium dendrites. The tensile deformed NCM811|PPL+FEC|Li mettery (referred to as PPL+FEC-mettery) delivered a significantly increased capacity (more than 33.2% at 1C, more than 23.6% at 2C and more than 44.8% at 5C) compared to tensile deformed PPL-mettery.