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Nanocomposite polymer electrolytes (CPEs) are promising materials for all-solid-state lithium metal batteries (LMBs) due to their enhanced ionic conductivities and stability to the lithium anode. MXenes are a new two-dimensional, 2D, family of early transition metal carbides and nitrides, which have a high aspect ratio and a hydrophilic surface. Herein, using a green, facile aqueous solution blending method, we uniformly dispersed small amounts of Ti 3 C 2 T x into a poly(ethylene oxide)/LiTFSI complex (PEO 20 -LiTFSI) to fabricate MXene-based CPEs (MCPEs). The addition of the 2D flakes to PEO simultaneously retards PEO crystallization and enhances its segmental motion. Compared to the 0D and 1D nanofillers, MXenes show higher efficiency in ionic conductivity enhancement and improvement in the performance of LMBs. The CPE with 3.6 wt% MXene shows the highest ionic conductivity at room temperature (2.2 × 10 −5 S m −1 at 28 °C). An LMB using MCPE with only 1.5 wt% MXene shows rate capability and stability comparable with that of the state-of-the-art CPELMBs. We attribute the excellent performance to the 2D geometry of the filler, the good dispersion of the flakes in the polymer matrix, and the functional group-rich surface. 

The MAB phases are atomically layered, ternary or quaternary transition metal (M) borides (TMBs), with the general formula (MB)_{2 z}A_x(MB₂)_y( z = 1–2; x = 1–2; y = 0–2), whose structures are composed of a transition M-B sublattices interleaved by A-atom (A = Al,Zn) mono- or bilayers. Most of the MAB phases were discovered before the 1990s, but recent discoveries of intriguing magnetocaloric properties, mechanical deformation behaviour, catalytic properties, and high-temperature oxidation resistance has led to their ‘re-discovery’. Herein, MAB phase synthesis is reviewed and their magnetic, electronic, thermal, and mechanical properties are summarized. Because the M-B layers in the MAB phases structurally resemble their corresponding binaries of the same M:B stoichiometry, the effects of the A-layers on properties are discussed. Inconsistencies in the literature are critically assessed to gain insights on the processing-structure-property relations, suggest fruitful avenues for future research, and identify limitations for prospective applications.