Method of producing lithium ion-storing/releasing material, lithium ion-storing/releasing material, and electrode structure and energy storage device using the material

Abstract

A method of producing a material capable of electrochemically storing and releasing a large amount of lithium ions is provided. The material is used as an electrode material for a negative electrode, and includes silicon or tin primary particles composed of crystal particles each having a specific diameter and an amorphous surface layer formed of at least a metal oxide, having a specific thickness. Gibbs free energy when the metal oxide is produced by oxidation of a metal is smaller than Gibbs free energy when silicon or tin is oxidized, and the metal oxide has higher thermodynamic stability than silicon oxide or tin oxide. The method of producing the electrode material includes reacting silicon or tin with a metal oxide, reacting a silicon oxide or a tin oxide with a metal, or reacting a silicon compound or a tin compound with a metal compound to react with each other.

1 . An electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions, the electrode material comprising silicon or tin primary particles composed of crystal particles each having a diameter of 5 nm to 200 nm and an amorphous surface layer having a thickness of 1 nm to 10 nm, wherein
 the amorphous surface layer of each of the primary particles is formed of at least a metal oxide;   Gibbs free energy when the metal oxide is produced by oxidation of a metal is smaller than Gibbs free energy when silicon or tin is oxidized; and   the metal oxide has higher thermodynamic stability than silicon oxide or tin oxide.   
     
     
         2 . An electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 1 , wherein a metal element accounts for 0.3 atomic % or more of the metal oxide in the primary particles. 
     
     
         3 . An electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 1 , wherein the silicon or tin primary particles are silicon particles. 
     
     
         4 . An electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 3 , wherein a crystallite size calculated from a half width of an Si(111) peak in an X-ray diffraction chart of the silicon particles and Sherrer's equation falls within a range of 20 to 60 nm. 
     
     
         5 . An electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 3 , wherein a molar ratio of silicon oxide to Si calculated from an X-ray photoelectron spectroscopy (XPS) measurement spectrum of the silicon particles is 0.05 to 7.0, and a ratio of an oxygen element to an Si element of the silicon particles measured with an energy dispersive X-ray spectrometer (EDX) of a scanning transmission electron microscope (STEM) is 0.05 to 0.8. 
     
     
         6 . An electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 3 , wherein the crystal particles of the silicon primary particles are formed into a network structure with fibrous (filamentous) substances, and a surface of each of the fibrous (filamentous) materials is coated with at least an oxide. 
     
     
         7 . An electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 6 , wherein the fibrous (filamentous) substances constituting the network structure each have a diameter in a range of 5 nm to 70 nm and a length in a range of 100 nm to 2 μm. 
     
     
         8 . An electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 6 , wherein the fibrous (filamentous) substances each have a core-shell structure, the core portion comprises a silicon crystal, and the shell portion comprises an amorphous silicon oxide or an amorphous metal oxide, provided that Gibbs free energy when the metal oxide is produced by oxidation of a metal is smaller than Gibbs free energy when silicon or tin is oxidized, and the metal oxide has higher thermodynamic stability than silicon oxide or tin oxide. 
     
     
         9 . An electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 6 , wherein the fibrous (filamentous) substances comprise amorphous silicon oxide. 
     
     
         10 . An electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 6 , wherein the fibrous (filamentous) substances comprise crystalline aluminum oxynitride. 
     
     
         11 . An electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 1 , wherein a metal element of the metal oxide comprises one or more types of metals selected from Li, Be, Mg, Al, Ca, Zr, Ba, Th, La, Ce, Nd, Sm, Eu, Dy, and Er. 
     
     
         12 . An electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 1 , wherein a metal element of the metal oxide comprises one or more types of metals selected from Li, Mg, Al, Ca, Zr, Ba, La, Ce, and Nd. 
     
     
         13 . A method of producing the electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 1 , comprising any one of the following steps:
 (i) reacting silicon or tin with a metal oxide;   (ii) reacting a silicon oxide or a tin oxide with a metal; and   (iii) reacting a silicon compound or a tin compound with a metal compound,   provided that Gibbs free energy when a metal oxide is produced by oxidation of a metal element of which the metal oxide or the metal is smaller than Gibbs free energy when silicon or tin is oxidized, and the metal oxide has higher thermodynamic stability than silicon oxide or tin oxide.   
     
     
         14 . A method of producing an electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 13 , wherein the reaction of silicon or tin with the metal oxide in the step (i) is
 (A) a reaction performed by introducing at least silicon or tin and the metal oxide in a powder state into thermal plasma obtained by turning an inert gas or a hydrogen gas into plasma, or   (B) a sintering reaction in spark plasma instantaneously generated by a spark discharge phenomenon caused by
 subjecting at least silicon or tin and the metal oxide to mechanical alloying treatment, 
 pressing a powder obtained by the mechanical alloying treatment, and 
 applying a pulsed current to gaps between the pressed powder particles at a low voltage under reduced pressure. 
   
     
     
         15 . A method of producing an electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 13 , wherein the reaction of the silicon oxide or the tin oxide with the metal in the step (ii) is at least one of
 (C) a reaction performed by introducing the metal, and the silicon oxide or the tin oxide, or silicon containing the silicon oxide or tin containing the tin oxide in a powder state into thermal plasma,   (D) a sintering reaction in spark plasma instantaneously generated by a spark discharge phenomenon caused by
 subjecting the metal, and the silicon oxide or the tin oxide, or silicon containing the silicon oxide or tin containing the tin oxide in a powder state to mechanical alloying treatment, 
 pressing a powder obtained by the mechanical alloying treatment, and 
 applying a pulsed current to gaps between the pressed powder particles at a low voltage under reduced pressure, 
   (E) a heating reaction in an inert gas or a hydrogen gas or under reduced pressure for a powder obtained by subjecting the metal, and the silicon oxide or the tin oxide, or silicon containing the silicon oxide or tin containing the tin oxide in a powder state to mechanical alloying treatment, and   (F) a heating reaction for a composite layer formed on a substrate by vapor deposition of the metal, and the silicon oxide or the tin oxide, or silicon containing the silicon oxide or tin containing the tin oxide.   
     
     
         16 . A method of producing an electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 13 , wherein in the reaction of the silicon compound or the tin compound with the metal compound in the step (iii),
 the silicon compound is a compound selected from silane, disilane, dichlorosilane, trichlorosilane, tetrachlorosilane, tetramethoxysilane, tetraethoxysilane, and tetrabutoxysilane,   the tin compound is a compound selected from tin tetrachloride, tetraethoxytin, tetrapropoxytin, and tetrabutoxytin,   the metal compound is a compound selected from trichloroaluminum, trimethoxyaluminum, triethoxyaluminum, tripropoxyaluminum, tributoxyaluminum, and aluminum isoperoxide, and   the compounds are heated in an inert gas atmosphere or hydrogen gas atmosphere so that a reaction temperature reaches 400 to 1,300° C.   
     
     
         17 . A method of producing an electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 15 , wherein the heating in the reaction (E) or (F) is performed by radiation with laser light or infrared light. 
     
     
         18 . A method of producing an electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 16 , wherein the heating is performed by radiation with laser light or infrared light. 
     
     
         19 . A method of producing an electrode material for a negative electrode of an energy storage device capable of electrochemically storing and releasing lithium ions according to  claim 16 , wherein the atmosphere is an atmosphere under reduced pressure. 
     
     
         20 . An electrode structure for a negative electrode of an energy storage device, comprising:
 a current collector; and   an electrode material layer (main active material layer) formed of a main active material as a powder material capable of storing and releasing lithium ions by an electrochemical reaction, wherein   the main active material is the electrode material according to  claim 1 .   
     
     
         21 . An electrode structure for a negative electrode of an energy storage device according to  claim 20 , wherein the electrode material layer is formed of the main active material and a binder. 
     
     
         22 . An electrode structure for a negative electrode of an energy storage device according to  claim 20 , wherein the electrode material layer is formed of the main active material, a conductive auxiliary material, and a binder. 
     
     
         23 . An electrode structure for a negative electrode of an energy storage device according to  claim 20 , wherein the electrode material layer has density in a range of 0.5 g/cm 3  or more and 3.5 g/cm 3  or less. 
     
     
         24 . An energy storage device comprising:
 a negative electrode using the electrode structure according to  claim 20 ;   a lithium ion conductor; and   a positive electrode, wherein   the energy storage device utilizes an oxidation reaction of lithium and a reduction reaction of lithium ions.   
     
     
         25 . An energy storage device according to  claim 24 , wherein the positive electrode is formed of at least a powder material which includes particles formed of a transition metal compound selected from a transition metal oxide, a transition metal phosphate compound, a lithium-transition metal oxide, and a lithium-transition metal phosphate compound, and is turned into a composite with a metal oxide having an amorphous phase.