The present application discloses a lithium-rich iron-based composite material and a preparation method and application thereof. The lithium-rich iron-based composite material includes a lithium-rich iron-based material having a molecular formular of aLiFeO.sub.2.Math.bLi.sub.2O.Math.cM.sub.xO.sub.y, where a, b, and c are numbers of moles, and 0?c/(a+b+c)?0.02, 1.8?b/a?2.1, M is a doping element, and 1?y/x?2.5. The lithium-rich iron-based composite material can provide abundant lithium, and the lithium-rich iron-based material has a high purity and low residual alkali on the surface, which lead to high capacity and good lithium supplementing effect, as well as good stability for storage and processing. The application of the lithium-rich iron-based composite material in a lithium-supplementing additive for cathodes, a cathode material, a cathode and a lithium-ion battery.

A ferrite particle having a spinel crystal structure belonging to a space group Fd-3m and having a ferrite composition represented by a specific formula, a carrier for an electrophotographic developer including the ferrite particle and a resin coating layer configured to coat a surface of the ferrite particle, an electrophotographic developer including the carrier for an electrophotographic developer and a toner, and a ferrite particle production method for producing the ferrite particle.

The present application provides a continuous reaction system, a ferromanganese phosphate precursor, a lithium iron manganese phosphate, a preparation method, and a secondary battery. A method for preparing a ferromanganese phosphate precursor provided in the present application is a continuous preparation method, thereby improving the production efficiency, and obtaining the ferromanganese phosphate precursor with small particle size, narrow particle size distribution, high crystallinity, monocrystal phase, regular appearance, high tap density, high batch stability, and high batch consistency.

A carrier core material formed with ferrite particles, the skewness Rsk of the particle is equal to or more than 0.40 but equal to or less than 0.20, and the kurtosis Rku of the particle is equal to or more than 3.20 but equal to or less than 3.50. Here, the maximum height Rz of the particle is equal to or more than 2.20 m but equal to or less than 3.50 m. Moreover, the ferrite particle contains at least either of Mn and Mg elements. In this way, cracking or chipping in a concave-convex portion of a particle surface is unlikely to occur, and moreover, the amount of coating resin used can be reduced without properties such as electrical resistance being lowered.

A method for producing MnZn ferrite comprising Fe, Mn and Zn as main components, and Ca, Si and Co, and at least one selected from the group consisting of Ta, Nb and Zr as sub-components, comprising a step of molding a raw material powder for the MnZn ferrite to obtain a green body, and a step of sintering the green body; the sintering step comprising a temperature-elevating step, a high-temperature-keeping step, and a cooling step; the cooling step including a slow cooling step of cooling in a temperature range of 1100 C. to 1250 C. at a cooling speed of 0 C./hour to 20 C./hour for 1 hours to 20 hours, and a cooling speed before and after the slow cooling step being higher than 20 C./hour; the MnZn ferrite having a volume resistivity of 8.5 .Math.m or more at room temperature, an average crystal grain size of 7 m to 15 m, and core loss of 420 kW/m.sup.3 or less between 23 C. and 140 C. at a frequency of 100 kHz and an exciting magnetic flux density of 200 mT.

Provided is a material that can be used as a potassium secondary battery positive electrode active material (particularly a potassium ion secondary battery positive electrode active material), other than Prussian blue, by using a potassium compound and a potassium ion secondary battery positive electrode active material comprising the potassium compound, the potassium compound being represented by general formula (1):

K.sub.nA.sub.kBO.sub.m,

wherein A is a positive divalent element in groups 7 to 11 of the periodic table; B is positive tetravalent silicon, germanium, titanium or manganese, excluding a case in which A is manganese and B is titanium, and a case in which A is cobalt and B is silicon; n is 1.5 to 2.5; and m is 3.5 to 4.5.

By using a potassium ion secondary battery positive electrode active material comprising a potassium compound represented by general formula (1): K.sub.nM.sub.m, wherein M is copper or iron, n is 0.5 to 3.5, and m is 1.5 to 2.5, provided is a potassium ion secondary battery positive electrode active material having higher theoretical discharge capacity and higher effective capacity than a potassium secondary battery using Prussian blue as a positive electrode active material.

By using a potassium ion secondary battery positive electrode active material comprising a potassium compound represented by general formula (1): K.sub.nM.sub.m, wherein M is copper or iron, n is 0.5 to 3.5, and m is 1.5 to 2.5, provided is a potassium ion secondary battery positive electrode active material having higher theoretical discharge capacity and higher effective capacity than a potassium secondary battery using Prussian blue as a positive electrode active material.

Provided are a ferrite material, a composite magnetic body, a coil component, and a power supply device, having high magnetic permeability. Ferrite is ferromagnetic and is expressed by a chemical formula Mn.sub.xSi.sub.yFe.sub.zO.sub.4-, where 0<x<1, y>0, z>0, x+y+z=3, and 0.5.

Core-shell particles containing crystalline iron oxide in the core and amorphous silicon dioxide in the shell and in which a) the shell contains from 5 to 40% by weight of silicon dioxide, b) the core contains b1) from 60 to 95% by weight of iron oxide and b2) from 0.5 to 5% by weight of at least one doping component selected from the group consisting of aluminum, calcium, copper, magnesium, silver, titanium, yttrium, zinc, tin and zirconium, c) where the % by weight indicated are based on the core-shell particles and the sum of a) and b) is at least 98% by weight of the core-shell particles, d) the core has lattice plane spacings of 0.20 nm, 0.25 nm and 0.29 nm, in each case+/0.02 nm, determined by means of HR-TEM.