This positive electrode active material for a non-aqueous electrolyte secondary battery contains a lithium-transition metal composite compound. The lithium-transition metal composite compound is represented by general formula Li.sub.xMn.sub.yNi.sub.zMe.sub.αO.sub.aF.sub.b (in the formula, 1≤x≤1.2, 0.4≤y≤0.8; 0≤z≤0.4, x+y+z=2, 0<α<0.05, 1.8≤a≤2, and 1.8≤a±b≤2.2 are satisfied, and Me represents at least two kinds of elements selected from metal elements other than Li, Mn, and Ni) and Me includes at least one kind of element having an ion radius of 0.6 Å or more.

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 positive electrode active material for an all-solid-state lithium ion secondary battery, containing: a lithium-metal composite oxide particle having a niobium solid solution layer and a center other than the niobium solid solution layer; and a coating layer coating at least a part of a surface of the lithium-metal composite oxide particle and formed of a compound containing lithium and niobium, an average thickness of the coating layer is 2 nm or more and 1 μm or less, and an average thickness of the niobium solid solution layer is 0.5 nm or more and 20 nm or less.

A positive electrode active material for an all-solid-state lithium ion secondary battery, containing: a lithium-metal composite oxide particle having a niobium solid solution layer and a center other than the niobium solid solution layer; and a coating layer coating at least a part of a surface of the lithium-metal composite oxide particle and formed of a compound containing lithium and niobium, an average thickness of the coating layer is 2 nm or more and 1 μm or less, and an average thickness of the niobium solid solution layer is 0.5 nm or more and 20 nm or less.

A binder composition for a non-aqueous secondary battery contains: a particulate polymer formed of a graft polymer that includes an acidic graft chain and that is obtained through a graft polymerization reaction of an acidic group-containing monomer and/or macromonomer with core particles containing a block copolymer that includes an aromatic vinyl block region formed of an aromatic vinyl monomer unit and an aliphatic conjugated diene block region formed of an aliphatic conjugated diene monomer unit; and an acidic group-containing water-soluble polymer that has a weight-average molecular weight of 200,000 or less.

A binder composition for a non-aqueous secondary battery contains: a particulate polymer formed of a graft polymer that includes an acidic graft chain and that is obtained through a graft polymerization reaction of an acidic group-containing monomer and/or macromonomer with core particles containing a block copolymer that includes an aromatic vinyl block region formed of an aromatic vinyl monomer unit and an aliphatic conjugated diene block region formed of an aliphatic conjugated diene monomer unit; and an acidic group-containing water-soluble polymer that has a weight-average molecular weight of 200,000 or less.

An object of the present invention is to provide a sulfide solid electrolyte having a reduced specific surface area; an electrode composite material, a slurry and a solid battery, in each of which the sulfide solid electrolyte is used; and a method of producing the sulfide solid electrolyte, and the present invention provides a sulfide solid electrolyte containing lithium (Li), phosphorus (P) and sulfur (S) elements, and also containing a crystal phase having peaks at positions of 2θ=23.2°±1.00° and 29.2°±0.500° in an X-ray diffraction pattern measured with CuKα1 radiation.

An object of the present invention is to provide a sulfide solid electrolyte having a reduced specific surface area; an electrode composite material, a slurry and a solid battery, in each of which the sulfide solid electrolyte is used; and a method of producing the sulfide solid electrolyte, and the present invention provides a sulfide solid electrolyte containing lithium (Li), phosphorus (P) and sulfur (S) elements, and also containing a crystal phase having peaks at positions of 2θ=23.2°±1.00° and 29.2°±0.500° in an X-ray diffraction pattern measured with CuKα1 radiation.

An electrochemical device, including a positive electrode. The positive electrode includes a positive current collector and a positive active material layer. The positive active material layer includes particles A and particles B. A circularity of a particle A is R.sub.A, a cross-sectional area of the particle A is S.sub.A, a circularity of a particle B is R.sub.B, a cross-sectional area of the particle B is S.sub.B, where R.sub.B<0.4≤R.sub.A and S.sub.B<20 μm.sup.2≤S.sub.A. Based on a total area of a cross section of the positive electrode in a direction perpendicular to the positive current collector, a ratio of a total area percent of the particles A to a total area percent of the particles B is 1:9 to 8:2. The electrochemical device exhibits excellent electrochemical performance, especially reduces the amount of generated gas and improves cycle stability of the electrochemical device.