Disclosed herein is a stabilised Na-ion oxide P3 phase of formula (I): P3-Na.sub.xM.sub.yO.sub.z Where, x>0.66, 0.8≤y≤1.0, z≤2; and M is selected from one or more of the group consisting of a 3d transition metal, a 4d transition metal, Al, Mg, B, Si, Sn, Sr and Ca. The stabilised Na-ion oxide P3 phase of formula (I) may be particularly useful as an active material in a Na-ion battery.

A lithium metal composite oxide having a layered structure, including at least lithium and an element X, wherein:the element X is at least one element selected from the group consisting of Co, Mn, Fe, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S and P; the lithium metal composite oxide contains single particles and satisfies all of requirements (1) to (5):(1): a volume-based 50% cumulative particle size D.sub.50 of the lithium metal composite oxide is 2 μm or more and 10 μm or less; (2): the single particles have, on at least a part of surfaces thereof, adhered fine particles, with the proviso that a maximum particle size of the adhered fine particles is smaller than a particle size of the single particles; (3): the particle size of the single particles is 0.2 to 1.5 times D.sub.50 of the lithium metal composite oxide; (4): a particle size of the adhered fine particles is 0.01 to 0.1 times the D.sub.50 of the lithium metal composite oxide; and (5): an average number of the adhered fine particles adhered per particle of the single particles is 1 or more and 30 or less as measured with respect to a range observable in an image obtained by scanning electron microscope.

The present exemplary embodiments relate to a positive electrode active material and a lithium secondary battery including the same. The positive active material for a lithium secondary battery according to an exemplary embodiment includes lithium metal oxide particles including lithium, nickel, cobalt, manganese and doping elements, and includes a first domain and a second domain inside the lithium metal oxide particles.

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.

This invention in one aspect relates to a method of synthesizing a self-assembled mixed-dimensional heterostructure including 2D metallic borophene and 1D semiconducting armchair-oriented graphene nanoribbons (aGNRs). The method includes depositing boron on a substrate to grow borophene thereon at a substrate temperature in an ultrahigh vacuum (UHV) chamber; sequentially depositing 4,4″-dibromo-p-terphenyl on the borophene grown substrate at room temperature in the UHV chamber to form a composite structure; and controlling multi-step on-surface coupling reactions of the composite structure to self-assemble a borophene/graphene nanoribbon mixed-dimensional heterostructure. The borophene/aGNR lateral heterointerfaces are structurally and electronically abrupt, thus demonstrating atomically well-defined metal-semiconductor heterojunctions.

Exemplary embodiments of positive electrode active materials in the form of single particles, and a method of preparing each of them, are provided. The single particles of the exemplary embodiments include single particles of a nickel-based lithium composite metal oxide, having a plurality of crystal grains, each having a size of 180 nm to 300 nm, as analyzed by a Cu Kα X-ray (X-rα). The single particles include a metal doped in the crystal lattice thereof. One embodiment includes a surface coating. The total content of the metal doped in the crystal lattice thereof and the metal of the metal oxide coated on the surface thereof is controlled in the range of 2500 ppm to 6000 ppm.

As for a secondary battery using lithium cobalt oxide as a positive electrode active material, the positive electrode active material with which a decrease in battery capacity due to repeated charge and discharge is inhibited is provided. Alternatively, a positive electrode active material particle which hardly deteriorates is provided. The positive electrode active material includes lithium, cobalt, oxygen, magnesium, aluminum, and fluorine and is a crystal represented by a layered rock-salt structure. The space group of the crystal is represented by R−3m. The concentration of fluorine in a surface portion of the crystal is higher than that inside the crystal. The concentration of magnesium in the surface portion of the crystal is higher than that inside the crystal. The atomic ratio of magnesium to aluminum in the surface portion of the crystal is higher than that inside the crystal.

A process for preparing a lithium nickel metal oxide is provided. The process comprises a step of high-energy milling a mixture of a nickel source, a lithium source and at least one additional metal source to form a high-energy milled intermediate, and subsequently calcining the high-energy milled intermediate to form the lithium nickel metal oxide.

In an embodiment a conversion element includes a first phase and a second phase, wherein the first phase comprises lutetium, aluminum, oxygen and a rare-earth element, wherein the second phase comprises Al.sub.2O.sub.3 single crystals, and wherein the conversion element comprises at least one groove.

Provided are methods of stabilizing MXene compositions using polyanionic salts so as to reduce the oxidation of the MXenes. Also provided are stabilized MXene compositions.