Fig. 4.

SEM images of Na metal morphology. Areal capacity of 1 and 3 mAh cm⁻² Na metal was deposited on a Cu surface using GFs–LE (a, b and c, d), GPE (e, f and g, h), GFs–GPE (i, j and k, l) and ANs–GPE (m, n and o, p) at current densities of 0.5 mA cm⁻² and 60 °C. The Cu/Na cells using (q, r) ANs–GPE and (s, t) GFs–GPE were stored at 60 °C for 10 days. The SEM images of Fig. 4b, d, f, h, j, l, n, p, r, t are magnified images of Fig. 4a, c, e, g, i, k, m, o, q, s. Scale bars, 10 μm in a, c, e, g, i, k, m, o, q, s; and 500 nm in b, d, f, h, j, l, n, p, r, t