Electrode, secondary battery, battery pack, and vehicle

A secondary battery, comprising:

• a liquid electrolyte;
• a positive electrode;
• and
• a negative electrode comprising an active material containing layer that contains
• active material particles capable of insertion and extraction of lithium ions, the active material particles comprising a niobium titanium oxide,
• polymer fibers having an average fiber diameter of 1 nm to 100 nm, and
• lithium-containing inorganic solid particles having lithium ion conductivity,
• wherein the lithium-containing inorganic solid particles include a phosphate compound,
• wherein the phosphate compound has a NASICON structure and is expressed as
• Li1+yAlxM2−x(PO4)3,
• wherein
• M represents at least one element selected from the group consisting of Ti, Ge, Sr, Sn, Zr, and Ca,
• x is not less than 0 and not more than 1, and
• y is not less than 0 and not more than 1,
• wherein a content of the polymer fibers in the active material containing layer ranges from 0.2 wt. % to 5 wt. %, and
• wherein a content of the inorganic solid particles in the active material containing layer ranges from 0.5 wt. % to 10 wt. %,
• wherein the polymer fibers are dispersed to form fine through holes in a mesh shape,
• wherein the liquid electrolyte is held by the mesh shape of the polymer fibers in the active material containing layer.