A secondary battery with favorable cycle performance is provided. Alternatively, a secondary battery with higher capacity is provided. A positive electrode active material layer including a first graphene layer, a second graphene layer, and a positive electrode active material. The first graphene layer includes a first region covering the positive electrode active material. The second graphene layer includes a second region covering the positive electrode active material and a third region overlapping with the first region. The first region includes a plane positioned between the positive electrode active material and the third region and formed of arranged six-membered carbon rings. The positive electrode active material includes a fourth region with a layered rock-salt structure. A lithium layer with a layered rock-salt structure included in the fourth region is substantially perpendicular to the plane formed of six-membered carbon rings and included in the second region.

The present invention relates to a carbonaceous material having a silicon element content of less than 200 ppm, a powder conductivity of 10.0 to 22.0 S/cm, a total amount of surface functional groups of 0.22 to 0.36 meq/g, and a pore volume of 0.10 to 0.20 cm.sup.3/g in terms of pores having a pore size of not less than 4 nm as measured by a BJH method.

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 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 solid electrolyte material according to the present disclosure includes Li, DC, Y, Sm, and X. The DC is at least one selected from the group consisting of Mg, Ca, Sr, Ba, and Zn. The X is at least one selected from the group consisting of F, Cl, Br, and I. A battery according to the present disclosure includes a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode. At least one selected from the group consisting of the positive electrode, the negative electrode, and the electrolyte layer includes the solid electrolyte material according to the present disclosure.

There is provided a sulfide solid electrolyte containing elemental lithium (Li), elemental phosphorus (P), elemental sulfur (S), and an elemental halogen (X). The mole ratio of the elemental lithium (Li) to the elemental phosphorus (P), Li/P, satisfies 3.7<Li/P<5.4. The mole ratio of the elemental sulfur (S) to the elemental phosphorus (P), S/P, satisfies 3.9<S/P<4.1. The mole ratio of the elemental halogen (X) to the elemental phosphorus (P), X/P, satisfies 0.7<X/P<2.4. The sulfide solid electrolyte includes a crystalline phase having an argyrodite-type crystal structure.

Provided are enhanced MXene materials made from MAX-phase precursors that comprise an excess of metal A. The resultant enhanced MXenes exhibit improved stability over periods of days and months, particularly when stored in aqueous media.

A producing method according to the present disclosure includes heat-treating a material mixture at higher than or equal to 150° C. and lower than or equal to 450° C., wherein the material mixture contains MX.sub.5 and at least one selected from the group consisting of Li.sub.2O.sub.2, Li.sub.2O, and LiOH, M is at least one selected from the group consisting of Ta and Nb, and X is at least one selected from the group consisting of Cl and Br.

There is provided a method for collecting and reusing an active material from positive electrode scrap. The positive electrode active material reuse method of the present disclosure includes (a) thermally treating positive electrode scrap comprising an active material layer on a current collector in air for thermal decomposition of a binder and a conductive material in the active material layer, to separate the current collector from the active material layer, and collecting an active material in the active material layer, (b) washing the collected active material using a lithium precursor aqueous solution which is basic in an aqueous solution and drying, and (c) annealing the washed active material to obtain a reusable active material.

A nanocomposite includes a plurality of nanoparticles, where each nanoparticle of the plurality of nanoparticles includes a TiO.sub.2 nanoparticle core characterized by a diameter between about 1 nm and about 20 nm and a surface .OH density below about 6.OH/nm.sup.2, and a nanoparticle shell conformally formed on surfaces of the TiO.sub.2 nanoparticle core. The nanoparticle shell is continuous and is thinner than about 2 nm. The nanoparticle shell includes a transparent material with a refractive index greater than about 1.7 for visible light. A valence band of the nanoparticle shell is more than about 0.1 eV lower than a valence band of the TiO.sub.2 nanoparticle core. A conduction band of the nanoparticle shell is more than about 0.5 eV higher than a conduction band of the TiO.sub.2 nanoparticle core.