A method of synthesizing soluble polyphosphides using shelf-stable reagents and common organic solvents is presented. A reaction between an alkali metal alkoxy compound or alkali metal alkyl thiolate compound, such as potassium ethoxide, and shelf stable red phosphorus generated soluble polyphosphides in a variety of organic solvents with the .sup.31P NMR spectrum being used to detect the species of polyphosphides produced.

A method of producing soluble polyphosphides from red phosphorous using solution chemistry is presented. A reaction between an alkali metal alkoxy compound or alkali metal alkyl thiolate compound, such as potassium ethoxide, and shelf stable red phosphorus generated soluble polyphosphides in a variety of organic solvents with the .sup.31P NMR spectrum being used to detect the species of polyphosphides produced.

A method of synthesizing soluble polyphosphides by activating red phosphorous using organic solvents is presented. A reaction between an alkali metal alkoxy compound or alkali metal alkyl thiolate compound, such as potassium ethoxide, and shelf stable red phosphorus generated soluble polyphosphides in a variety of organic solvents with the .sup.31P NMR spectrum being used to detect the species of polyphosphides produced.

A method of activating red phosphorous using organic solvents to synthesize soluble polyphosphides is presented. A reaction between an alkali metal alkoxy compound or alkali metal alkyl thiolate compound, such as potassium ethoxide, and shelf stable red phosphorus generated soluble polyphosphides in a variety of organic solvents with the .sup.31P NMR spectrum being used to detect the species of polyphosphides produced.

A method of using alkali metal compounds and organic solvents to activate red phosphorous for synthesizing soluble polyphosphides is presented. A reaction between an alkali metal alkoxy compound or alkali metal alkyl thiolate compound, such as potassium ethoxide, and shelf stable red phosphorus generated soluble polyphosphides in a variety of organic solvents with the .sup.31P NIVIR spectrum being used to detect the species of polyphosphides produced.

A method of producing soluble polyphosphides from red phosphorous using alkali metal compounds and organic solvents is presented. A reaction between an alkali metal alkoxy compound or alkali metal alkyl thiolate compound, such as potassium ethoxide, and shelf stable red phosphorus generated soluble polyphosphides in a variety of organic solvents with the .sup.31P NMR spectrum being used to detect the species of polyphosphides produced.

A cathode material for a lithium-ion secondary battery of the present invention includes active material secondary particles formed by aggregating central particles including primary particles of a cathode active material represented by General Formula Li.sub.aA.sub.xBO.sub.4 (here, A represents at least one element selected from the group consisting of Mn, Fe, Co, and Ni, B represents at least one element selected from the group consisting of P, Si, and S, 0a<4, and 0<x<1.5) and a carbonaceous film, wherein at least a portion of surfaces of the primary particles are coated with the carbonaceous film, and the carbonaceous film is obtained by thermal decomposition of an organic compound, in which, in a charge and discharge cycle test at 60 C. of the lithium-ion secondary battery including a cathode including the active material secondary particles and an anode made of graphite, an amount of the element represented by A penetrates into or is precipitated on the anode after 500 cycles, is 600 ppm or less of a mass of the active material secondary particles.