materials like metal shrouds are heavy, bulky, and easy to corrode. [5] As a result, the development of new EMI shielding materials has become an urgent demand for material science and engineering.Carbon-based materials, like graphene [6] and carbon nanotubes, [7] have attracted much attention as promising effective EMI shielding materials due to their high conductivity, relatively low density, and corrosion resistance. Incorporating conductive fillers with polymer matrix has been developed as a feasible alternative solution for EMI shielding materials due to its tunable structure, good processability, and mechanical properties. [8][9][10] Nevertheless, despite promising advances have been achieved for carbon-based EMI shielding materials, the incorporation of polymer inevitably accompanied with deteriorated performance due to the introduction of insulating volume in conductive network. Generally, carbon-polymer composite EMI shielding materials usually require millimeter-scale thickness to achieve satisfying shielding effectiveness, which limits their applications in many areas, especially aerospace and smart microelectronic devices. It is still an enormous challenge to obtain desirable EMI shielding efficiency at a small thickness and low density. [11][12][13] Early transition metal carbides, nitrides, and carbonitrides, known as MXenes, [14] are a new class of 2D materials which have great advantages like metallic conductivity, high specific capacitance, and excellent mechanical properties. [15,16] MXenes have demonstrated promising applications in various areas including supercapacitors, [17] batteries, [18] water desalination, [19] and sensors. [20] During the synthesis of MXene, various functional groups (e.g., O, OH, and F, denoted as -T x in the chemical formula of MXenes like Ti 3 C 2 T x ) were deposited at its surface. [21] As a result, MXene presents excellent hydrophilicity and dispersity in aqueous solution, endowing it with good solution processing capability with polymer matrix. [22,23] Very recently, the application of MXene in EMI shielding has been reported. Shahzad et al. prepared Ti 3 C 2 T x film and Ti 3 C 2 T x -sodium alginate (SA) film through vacuum assisted filtration, among them pristine Ti 3 C 2 T x film exhibited a superior EMI shielding efficiency of 92 dB. [24] Sun fabricated highly conductive Ti 3 C 2 T x at polystyrene composites through electrostatic assembly of negatively charged Ti 3 C 2 T x nanoflakes on positively charged polystyrene microspheres, the obtained composite film exhibited an outstanding EMI shielding Ultrathin and high-performance electromagnetic interference (EMI) shielding materials are urgently demanded for modern microelectronic devices. 2D metal carbides (MXenes) are considered as a promising EMI shielding material due to its metallic conductivity. In this study, sodium alginate is applied as interlayer spacer for Ti 3 C 2 T x nanosheets, which not only prevents the restacking of lamella structure but also serves as building blocks for the sponge-like s...