A positive electrode (100) includes a positive electrode current collector (110), a positive electrode mixture (120), and a mixture (130). The positive electrode current collector (110) has a first surface (112). The first surface (112) of the positive electrode current collector (110) includes a first region (112a), a second region (112b), and a third region (112c). The positive electrode (100) satisfies the following expression (1).

0≤L3/(L1+L3)≤0.075  (1)

Here, L1 is a length of the positive electrode (100) of the first region (112a) of the positive electrode (100) in one direction (first direction (X)), and L3 is a length of the third region (112c) of the positive electrode (100) in the one direction (first direction (X)).

A secondary battery is provided including an electrode wound body housed in a battery can, with the electrode wound body having a structure including a band-shaped positive electrode and a band-shaped negative electrode laminated and wound with a separator interposed therebetween, where the positive electrode includes a positive electrode active material layer on both sides of a band-shaped positive electrode foil, the negative electrode includes a negative electrode active material layer on both sides of a band-shaped negative electrode foil, the electrode wound body includes a positive electrode tab at a central part of the positive electrode, includes a negative electrode tab on a winding end side of the negative electrode, and includes a foil tab in a flat plate shape on a winding start side of either one or both of the positive electrode and the negative electrode.

A secondary battery includes: an electrode assembly; a case accommodating the electrode assembly; a current collector plate welded to the electrode assembly and the case; and a cap plate on the current collector plate and sealing the case.

A secondary battery includes: an electrode assembly; a case accommodating the electrode assembly; a current collector plate welded to the electrode assembly and the case; and a cap plate on the current collector plate and sealing the case.

A tab, a preparation method thereof, and a battery including the tab are disclosed. The tab is a copper foil material, a surface of the copper foil material having a large compressive stress is an S surface, a surface having a small compressive stress is an M surface, and only the M surface is provided with an indentation or a reinforcing rib. In the preparation method of the tab of the disclosure, the S surface/M surface of the copper foil material are identified, and it is ensured that a feed direction is oriented so that the M surface faces outward (or inward), and winding/unwinding directions of each process and a mounting direction of an embossing device are reasonably fixed, so as to ensure that a tab emboss pattern of a product is pressed on the M surface of the copper foil material rather than the S surface or both surfaces.

A negative electrode comprises a negative electrode collector, a first negative electrode mixture layer that is provided on the surface of the negative electrode collector, and a second negative electrode mixture layer that faces the positive electrode; the first negative electrode mixture layer and the second negative electrode mixture layer contain graphite particles; the ratio of the void fraction (S2) among the graphite particles in the second negative electrode mixture layer to the void fraction (S1) among the graphite particles in the first negative electrode mixture layer, namely S2/S1 is from 1.1 to 2.0; the ratio of the packing density (D2) of the second negative electrode mixture layer to the packing density (D1) of the first negative electrode mixture layer, namely D2/D1 is from 0.9 to 1.1; and the separator has a thickness of 10 μm or less, while having a porosity of from 25% to 45%.

A negative electrode comprises a negative electrode collector, a first negative electrode mixture layer that is provided on the surface of the negative electrode collector, and a second negative electrode mixture layer that faces the positive electrode; the first negative electrode mixture layer and the second negative electrode mixture layer contain graphite particles; the ratio of the void fraction (S2) among the graphite particles in the second negative electrode mixture layer to the void fraction (S1) among the graphite particles in the first negative electrode mixture layer, namely S2/S1 is from 1.1 to 2.0; the ratio of the packing density (D2) of the second negative electrode mixture layer to the packing density (D1) of the first negative electrode mixture layer, namely D2/D1 is from 0.9 to 1.1; and the separator has a thickness of 10 μm or less, while having a porosity of from 25% to 45%.

An electrochemical apparatus includes a first electrode plate and a first tab. The first electrode plate includes a current collector and an active material layer disposed on the current collector. The current collector includes a first surface, a first side and a second side opposite to the first side; the first surface is provided with a first blank region and the first tab is electrically connected to the first blank region and protrudes from the first side. A first tab adhesive is provided on the first tab, where the first tab adhesive includes a first adhesive layer, and the first adhesive layer includes a third side facing toward the second side. A minimum distance D.sub.1 mm between the third side and the second side and a distance W mm between the first side and the second side satisfy D.sub.1<W.

An electrochemical apparatus includes a first electrode plate and a first tab. The first electrode plate includes a current collector and an active material layer disposed on the current collector. The current collector includes a first surface, a first side and a second side opposite to the first side; the first surface is provided with a first blank region and the first tab is electrically connected to the first blank region and protrudes from the first side. A first tab adhesive is provided on the first tab, where the first tab adhesive includes a first adhesive layer, and the first adhesive layer includes a third side facing toward the second side. A minimum distance D.sub.1 mm between the third side and the second side and a distance W mm between the first side and the second side satisfy D.sub.1<W.

A cell unit includes a positive electrode current collector, a positive electrode active material layer, a separator, a negative electrode active material layer and a negative electrode current collector which are laminated on one another, the cell unit comprising a frame member arranged between the positive electrode current collector and an opposing negative electrode current collector and fixing a peripheral edge portion of the separator, and an electronic component for detecting the state inside the cell unit, wherein the electronic component is arranged in a region between the positive electrode current collector and the negative electrode current collector, and the electronic component arranged in the region is electrically connected to the positive electrode current collector and the negative electrode current collector.