A negative active material for a rechargeable lithium battery includes a carbon-based active material including highly crystalline natural graphite and artificial graphite. The carbon-based active material has a peak intensity ratio (P2/P4) of about 0.3 to about 0.4, wherein P2 refers to the 101 peak of a rhombohedral crystal grain and P4 refers to the 101 peak of a hexagonal crystal grain, as measured by X-ray diffraction.

A negative active material for a rechargeable lithium battery includes a carbon-based active material including highly crystalline natural graphite and artificial graphite. The carbon-based active material has a peak intensity ratio (P2/P4) of about 0.3 to about 0.4, wherein P2 refers to the 101 peak of a rhombohedral crystal grain and P4 refers to the 101 peak of a hexagonal crystal grain, as measured by X-ray diffraction.

An embodiment is directed to a solid state electrolyte-comprising Li or Li-ion battery cell, comprising an anode electrode, a cathode electrode with an areal capacity loading that exceeds around 3.5 mAh/cm.sup.2, an ionically conductive separator layer that electrically separates the anode and cathode electrodes, and one or more solid electrolytes ionically coupling the anode and the cathode, wherein at least one of the one or more solid electrolytes or at least one solid electrolyte precursor of the one or more solid electrolytes is infiltrated into the solid state Li or Li-ion battery cell as a liquid.

An embodiment is directed to a solid state electrolyte-comprising Li or Li-ion battery cell, comprising an anode electrode, a cathode electrode with an areal capacity loading that exceeds around 3.5 mAh/cm.sup.2, an ionically conductive separator layer that electrically separates the anode and cathode electrodes, and one or more solid electrolytes ionically coupling the anode and the cathode, wherein at least one of the one or more solid electrolytes or at least one solid electrolyte precursor of the one or more solid electrolytes is infiltrated into the solid state Li or Li-ion battery cell as a liquid.

The present invention provides a binder for a secondary battery that can reduce the initial resistance value of the secondary battery. A binder for a secondary battery comprising a polymer compound, wherein the polymer compound contains repeating units represented by formulae (1), (2), and (3):

##STR00001## in formula (1), R.sup.1 is a hydrogen atom or a methyl group, and M is a hydrogen atom or an alkali metal atom; and in formula (3), R.sup.2 is a hydrogen atom or a methyl group; and when a total ratio of repeating units constituting the polymer compound is taken as 100 mol %, a total ratio of the repeating unit represented by formula (3) is less than 2 mol %.

The present invention provides a binder for a secondary battery that can reduce the initial resistance value of the secondary battery. A binder for a secondary battery comprising a polymer compound, wherein the polymer compound contains repeating units represented by formulae (1), (2), and (3):

##STR00001## in formula (1), R.sup.1 is a hydrogen atom or a methyl group, and M is a hydrogen atom or an alkali metal atom; and in formula (3), R.sup.2 is a hydrogen atom or a methyl group; and when a total ratio of repeating units constituting the polymer compound is taken as 100 mol %, a total ratio of the repeating unit represented by formula (3) is less than 2 mol %.

A lithium secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. The negative electrode is an electrode in which lithium metal deposits during charging and the lithium metal dissolves during discharging, the separator includes a substrate, a first layer disposed on a first side of the substrate, and a second layer disposed on a second side of the substrate, the first layer includes particles of phosphate containing lithium, the second layer includes a polymer and/or inorganic particles other than the particles of the phosphate, and the polymer is at least one selected from the group consisting of aromatic polyamide, aromatic polyimide, and aromatic polyamide-imide.

A lithium secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. The negative electrode is an electrode in which lithium metal deposits during charging and the lithium metal dissolves during discharging, the separator includes a substrate, a first layer disposed on a first side of the substrate, and a second layer disposed on a second side of the substrate, the first layer includes particles of phosphate containing lithium, the second layer includes a polymer and/or inorganic particles other than the particles of the phosphate, and the polymer is at least one selected from the group consisting of aromatic polyamide, aromatic polyimide, and aromatic polyamide-imide.

A negative electrode material includes silicon composite particles. The silicon composite particles include amorphous silicon particles and a buffer phase. The amorphous silicon particles are dispersed in the buffer phase. A non-uniformity of the amorphous silicon particles dispersed in the buffer phase is less than or equal to 30%. Also, an electronic device including the negative electrode material.

A first electrode current collector is joined to a multilayer of a positive electrode core in a part including no positive electrode active material layer of the first electrode core, by ultrasonic welding in a joint area. The joint area, at which the multilayers of the first electrode core where the first electrode cores are stacked is joined to the first electrode current collector by ultrasonic welding, includes a plurality of core recesses. A core projection is formed between each adjacent pair of the plurality of core recesses of the multilayer of the first electrode core with the first electrode core flexed in a convex shape. A gap in an arc shape is formed between the adjacent pair of the layers of the first electrode core forming the core projection. The gap has a length decreasing from an apex to a bottom of the core projection.