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.

The present invention provides a solid-phase catalyst for decomposing hydrogen peroxide comprising a permanganate salt and a manganese (II) salt. The solid-phase catalyst stays a solid state in the form of nanoparticles at the time of hydrogen peroxide decomposition, and thus can be recovered for reuse and also has an excellent decomposition rate. In the method for producing a solid-phase catalyst for decomposing hydrogen peroxide according to the present invention, a solid-phase catalyst is produced from a solution containing a permanganate salt, a manganese (II) salt, and an organic acid, so that the produced solid-phase catalyst is precipitated as a solid component even after a catalytic reaction, and thus is reusable and environmentally friendly, and cost reduction can be achieved through the simplification of a catalyst production technique.

To provide metal-containing trimanganese tetraoxide combined particles with which a metal-substituted lithium manganese oxide excellent as a cathode material for a lithium secondary battery can be obtained, and their production process. Metal-containing trimanganese tetraoxide combined particles containing a metal element (excluding lithium and manganese). Such metal-containing trimanganese tetraoxide combined particles can be obtained by a production process comprising a crystallization step of crystalizing a metal-substituted trimanganese tetraoxide not by means of metal-substituted manganese hydroxide from a manganese salt aqueous solution containing manganese ions and metal ions other than manganese.

A method for producing lithium manganese oxide that is a precursor of a lithium adsorbent under atmospheric pressure is provided. The method for producing a precursor of a lithium adsorbent comprises the following steps (1) to (3): (1) A 1.sup.st mixing step of mixing a manganese salt and alkali hydroxide, so as to obtain a 1.sup.st slurry containing manganese hydroxide; (2) a 2.sup.nd mixing step of adding lithium hydroxide to the 1.sup.st slurry and then mixing the mixture to obtain a 2.sup.nd slurry; and (3) an oxidation step of adding an oxidizing agent to the 2.sup.nd slurry, so as to obtain a precursor of a lithium adsorbent. The method for producing a precursor of a lithium adsorbent comprises these steps, so that a precursor of a lithium adsorbent can be produced under atmospheric pressure. Therefore, a precursor of a lithium adsorbent can be produced at a limited cost.

Provided is a lithium secondary battery having excellent charge-discharge cycle performance at high temperatures and having low resistance and high power. A spinel-type lithium manganese oxide including a phosphate, the spinel-type lithium manganese oxide being represented by chemical formula: Li.sub.1+XMn.sub.2?X?YM.sub.YO.sub.4 (where 0.02?X?0.20, 0.05?Y?0.30, and M represents Al or Mg), wherein the volume of pores having a size of 0.6 ?m or less is 0.003 cm.sup.3/g or more and 0.2 cm.sup.3/g or less, and the relative standard deviation of size of secondary particles is 25% or more and 45% or less, a method for producing the spinel-type lithium manganese oxide and applications of the spinel-type lithium manganese oxide.

Surface modified lithium-containing composite oxide particles include base material particles of lithium-containing composite oxide, zirconium hydroxide or zirconium oxide, and at least one lithium salt selected from the group consisting of Li.sub.2ZrF.sub.6, Li.sub.2TiF.sub.6, Li.sub.3PO.sub.4, Li.sub.2SO.sub.4 and Li.sub.2SO.sub.4.H.sub.2O. The zirconium hydroxide or zirconium oxide, and the at least one lithium salt are attached to a surface of the base material particle. The lithium-containing composite oxide is represented by the formula: Li.sub.pN.sub.xM.sub.yO.sub.zF.sub.a. N is at least one element selected from the group consisting of Co, Mn and Ni; M is at least one element selected from the group consisting of Al, elements of group 2, and transition metal elements other than N; 0.9<p<1.1; 0.85<x<1.0; 0<y<0.15; 1.9<z<2.1; x+y=1; and 0<a<0.05.

Provided are a silicate modified manganese-based material and a preparation method and application thereof. The silicate modified manganese-based material has a nanoscale needle like structure, and is prepared from a solution containing a manganese source and a soluble silicate source through an oxidation-reduction reaction and then a hydrothermal reaction. The manganese source includes a divalent manganese source and a heptavalent manganese source, with Mn (II) and Mn (VII) in a molar ratio of 0.5-5.5 to 1. The present disclosure uses silicate to regulate manganese oxides, significantly reducing the particle size of the manganese-based material, generating manganese vacancies, and changing the surface manganese valence state. An advanced oxidation system formed by the silicate modified manganese-based material and an oxidant has high removal rate and reaction rate for various organic compounds.

Provided are polycrystalline lithium manganese oxide particles represented by Chemical Formula 1 and a method of preparing the same:
Li.sub.(1+x)Mn.sub.(2-x-y-f)Al.sub.yM.sub.fO.sub.(4-z)<Chemical Formula 1> where M is sodium (Na), or two or more mixed elements including Na, 0x0.2, 0<y0.2, 0<f0.2, and 0z0.2. According to an embodiment of the present invention, limitations, such as the Jahn-Teller distortion and the dissolution of Mn.sup.2+, may be addressed by structurally stabilizing the polycrystalline lithium manganese oxide particles. Thus, life characteristics and charge and discharge capacity characteristics of a secondary battery may be improved.

Provided are a cathode active material including polycrystalline lithium manganese oxide and a sodium-containing coating layer on a surface of the polycrystalline lithium manganese oxide, and a method preparing the same. Since the cathode active material according to an embodiment of the present invention may prevent direct contact between the polycrystalline lithium manganese oxide and an electrolyte solution by including the sodium-containing coating layer on the surface of the polycrystalline lithium manganese oxide, the cathode active material may prevent side reactions between the cathode active material and the electrolyte solution. In addition, since limitations, such as the Jahn-Teller distortion and the dissolution of Mn.sup.2+, may be addressed by structurally stabilizing the polycrystalline lithium manganese oxide, tap density, life characteristics, and charge and discharge capacity characteristics of a secondary battery may be improved.

A process of purifying acetic acid is provided. The process includes feeding a stream of acetic acid into a distillation column and distilling acetic acid in the presence of an oxidizing agent in the distillation column, to oxidize oxidizable impurities in the acetic acid, wherein the oxidizing agent is an oxidant capable of cleaving CC bonds. The process further includes removing a distilled acetic acid stream from the distillation column. Further processes for purifying acetic acid and systems for purifying acetic acid are also provided.