Negative electrode material for non-aqueous electrolyte secondary battery and method of producing negative electrode active material particles

Abstract

A negative electrode material for a non-aqueous electrolyte secondary battery contains negative electrode active material particles containing a silicon compound expressed by SiO x , where 0.5≤x≤1.6, and a coating layer composed of an organic polymer coating the silicon compound, the silicon compound containing a lithium compound on its surface or inside. As a result, a negative electrode material for a non-aqueous electrolyte secondary battery can increase the battery capacity and improve the cycle performance and battery initial efficiency.

1 . A negative electrode material for a non-aqueous electrolyte secondary battery, comprising
 negative electrode active material particles comprising a silicon compound expressed by SiO x , where 0.5≤x≤1.6, and a coating layer composed of an organic polymer coating the silicon compound, wherein   the silicon compound contains Li 2 SiO 3  inside.   
     
     
         2 . The negative electrode material for a non-aqueous electrolyte secondary battery according to  claim 1 , wherein the organic polymer contains at least one of a fluoroethylene group, a carboxyl group, a hydroxyl group, and a carbonate group within its molecule. 
     
     
         3 . The negative electrode material for a non-aqueous electrolyte secondary battery according to  claim 1 , wherein the organic polymer comprises at least one polymer selected from the group consisting of polyvinyl alcohol, polycarbonate, polyvinylidene fluoride, and polyvinylidene tetrafluoride. 
     
     
         4 . The negative electrode material for a non-aqueous electrolyte secondary battery according to  claim 1 , wherein a content of the organic polymer is 0.01 mass % or more and less than 5 mass % with respect to the whole negative electrode active material particles. 
     
     
         5 . The negative electrode material for a non-aqueous electrolyte secondary battery according to  claim 1 , wherein at least a part of the organic polymer has an island-shaped structure. 
     
     
         6 . The negative electrode material for a non-aqueous electrolyte secondary battery according to  claim 1 , wherein the silicon compound further contains at least one lithium compound on its surface, and the lithium compound is at least one selected from the group consisting of Li 2 CO 3 , Li 2 O, and LiF. 
     
     
         7 . The negative electrode material for a non-aqueous electrolyte secondary battery according to  claim 1 , wherein the silicon compound further contains at least one lithium compound selected from the group consisting of Li 4 SiO 4  and Li 6 Si 2 O 7  inside. 
     
     
         8 . The negative electrode material for a non-aqueous electrolyte secondary battery according to  claim 1 , wherein the silicon compound is at least partially coated with a carbon compound. 
     
     
         9 . The negative electrode material for a non-aqueous electrolyte secondary battery according to  claim 8 , wherein a coverage of the carbon compound is 15 mass % or less with respect to a total of the silicon compound and the carbon compound. 
     
     
         10 . The negative electrode material for a non-aqueous electrolyte secondary battery according to  claim 8 , wherein the silicon compound satisfies 0.05≤A/B≤3.00 when subjected to X-ray photoelectron spectroscopy (XPS) on its surface layer where A is a peak area of a peak when a C1s binding energy is about 287.5±1.0 eV, and B is a peak area of a peak when the C1s binding energy is about 284.0±1.0 eV. 
     
     
         11 . The negative electrode material for a non-aqueous electrolyte secondary battery according to  claim 8 , wherein the silicon compound satisfies 0.10≤A/B≤1.00 when subjected to X-ray photoelectron spectroscopy (XPS) on its surface layer where A is a peak area of a peak when a C1s binding energy is about 287.5±1.0 eV, and B is a peak area of a peak when the C1s binding energy is about 284.0±1.0 eV. 
     
     
         12 . The negative electrode material for a non-aqueous electrolyte secondary battery according to claim  1 , wherein the coating layer composed of the organic polymer contains a particulate carbon-based material having a median size smaller than that of the silicon compound. 
     
     
         13 . The negative electrode material for a non-aqueous electrolyte secondary battery according to  claim 1 , wherein the silicon compound exhibits a diffraction peak having a half width (2θ) of 1.2° or more, the diffraction peak being attributable to an (111) crystal face and obtained by X-ray diffraction, and a crystallite size attributable to the crystal face is 7.5 nm or less. 
     
     
         14 . The negative electrode material for a non-aqueous electrolyte secondary battery according to  claim 1 , wherein the silicon compound containing Li 2 SiO 3  inside is produced by a step including an electrochemical manner. 
     
     
         15 . A negative electrode for a non-aqueous electrolyte secondary battery, comprising a negative electrode material according to  claim 1 . 
     
     
         16 . The negative electrode for a non-aqueous electrolyte secondary battery according to  claim 15 , further comprising a carbon-based negative electrode material. 
     
     
         17 . The negative electrode for a non-aqueous electrolyte secondary battery according to  claim 16 , wherein a median size Y of the silicon compound and a median size X of the carbon-based negative electrode material satisfy X/Y≥1. 
     
     
         18 . A non-aqueous electrolyte secondary battery comprising a negative electrode according to  claim 15 . 
     
     
         19 . A method of producing negative electrode active material particles contained in a negative electrode material for a non-aqueous electrolyte secondary battery, comprising the steps of:
 producing a silicon compound expressed by SiO x  where 0.55≤x≤1.6;   inserting lithium into the silicon compound and thereby forming a lithium compound that includes Li 2 SiO 3  at least inside the silicon compound to modify the silicon compound; and   coating the silicon compound with a coating layer composed of an organic polymer to produce the negative electrode active material particles.   
     
     
         20 . The method of producing negative electrode active material particles according to  claim 19 , wherein the step of modifying the silicon compound is performed in an electrochemical manner.