Positively Charged Silicon for Lithium-Ion Batteries

Abstract

This invention relates to a negative electrode material for lithium-ion batteries comprising silicon and having a chemically treated or coated surface influencing the zeta potential of the surface. The active material consists of particles or particles and wires comprising a core ( 11 ) comprising silicon, wherein the particles have a positive zeta potential in an interval between pH 3.5 and 9.5, and preferably between pH 4 and 9.5. The core is either chemically treated with an amino-functional metal oxide, or the core is at least partly covered with O y SiH x groups, with 1<x<3, 1<y<3, and x>y, or is covered by adsorbed inorganic nanoparticles or cationic multivalent metal ions or oxides.

1 - 38 . (canceled) 
     
     
         39 . A negative electrode material for a lithium rechargeable battery, the material comprising a core comprising silicon, wherein the surface of the core carries O y SiH x  groups, with 1<x<3, 1≦y≦3, and x>y, and wherein the material has a positive zeta potential in an interval between pH 3.5 and 9.5. 
     
     
         40 . A negative electrode material for a lithium rechargeable battery, the material comprising a core comprising silicon, wherein the surface of the core is at least partly covered by a coating comprising inorganic nanoparticles, and wherein the material has a positive zeta potential in an interval between pH 3.5 and 9.5. 
     
     
         41 . The negative electrode material of  claim 40 , wherein the inorganic nanoparticles comprise an aluminum compound, a zinc compound or an antimony compound. 
     
     
         42 . The negative electrode material of  claim 41 , wherein the aluminum compound is either aluminum or Al 2 O 3 , the zinc compound is either zinc or zinc oxide, and the antimony compound is either antimony or antimony oxide. 
     
     
         43 . The negative electrode material of  claim 40 , wherein the nanoparticles form a first coating layer on the core, the first coating layer having a thickness of less than 10 nm. 
     
     
         44 . The negative electrode material of  claim 43 , wherein the particles further comprise a second coating layer located between the core and the nanoparticles, the second coating layer comprising either carbon or aluminum. 
     
     
         45 . The negative electrode material of  claim 43 , wherein the first coating layer has a thickness between 1 and 5 nm. 
     
     
         46 . The negative electrode material of  claim 43 , wherein the first coating layer is either conformal or porous. 
     
     
         47 . The negative electrode material of  claim 44 , wherein either one or both of the first and second coating layer is electrochemically active. 
     
     
         48 . The negative electrode material of  claim 40 , wherein the nanoparticles comprise a precursor material susceptible of being converted to aluminum, zinc or antimony by reduction. 
     
     
         49 . A negative electrode material for a lithium rechargeable battery, the material comprising a core comprising silicon, wherein the surface of the core is at least partly covered by adsorbed cationic multivalent metal ions, and wherein the material has a positive zeta potential in an interval between pH 3.5 and 9.5. 
     
     
         50 . The negative electrode material of  claim 49 , wherein the metal ions are selected from the group consisting of Al-, Sb-, Fe-, Ti- and Zn-ions and combinations thereof. 
     
     
         51 . A negative electrode material for a lithium rechargeable battery, the material comprising a core comprising silicon, wherein the surface of the core is at least partly covered by silanol groups covalently bound to amino-functional metal compounds, wherein the metal compound is selected from the group consisting of Si, Al and Ti and combinations thereof, and wherein the material has a positive zeta potential in an interval between pH 3.5 and 9.5. 
     
     
         52 . A negative electrode material for a lithium rechargeable battery, the material comprising a core comprising silicon, wherein the surface of the core is at least partly covered by adsorbed nanoparticles of cationic multivalent metal oxides, and wherein the material has a positive zeta potential in an interval between pH 3.5 and 9.5. 
     
     
         53 . The negative electrode material of  claim 52 , wherein the metal oxides are selected from the group consisting of Al-oxide, Ca-oxide, Mg-oxide, Pb-oxide, Sb-oxide, Fe-oxide, Ti-oxide, Zn-oxide and In-hydroxide and combinations thereof. 
     
     
         54 . The negative electrode material of  claim 40 , wherein the material has a positive zeta potential in an interval between pH 4 and 9.5. 
     
     
         55 . The negative electrode material of  claim 40 , wherein the material has a point of zero-charge at pH 4 or higher. 
     
     
         56 . The negative electrode material of  claim 40 , comprising either particles or a mixture of particles and wires. 
     
     
         57 . The negative electrode material of  claim 56 , wherein both the particles and the wires are nano-sized, and wherein the average particle size of the particles is at least 5 times the average width of the wires. 
     
     
         58 . The negative electrode material of  claim 40 , wherein the core has an average particle size between 20 nm and 200 nm and comprises either
 pure silicon; or   a silicon monoxide powder, which comprises a mixture at nanometric scale of Si and SiO 2 ; or   silicon having a SiO x  surface layer, with 0<x<2, the surface layer having an average thickness between 0.5 nm and 10 nm; or   a homogeneous mixture of silicon- and metal-oxides, having the formula SiO x  (M a O b ) y , with 0<x<1 and 0≦y<1, wherein a and b are selected to provide electroneutrality, and wherein M is selected from the group consisting of Ca, Mg, Li, Al, and Zr; or   an alloy Si—X, wherein X is either one or more metals selected from the group consisting of Sn, Ti, Fe, Ni, Cu, Co and Al.   
     
     
         59 . The negative electrode material of  claim 40 , wherein the material has a BET value between 1 and 60 m 2 /g. 
     
     
         60 . A process for preparing the negative electrode material according to  claim 49 , comprising:
 providing a nanosized silicon material;   dispersing the silicon material in water;   providing a quantity of cationic multivalent metal ions in the dispersion,   adjusting the pH of the dispersion to a value between 2 and 3.5, and thereafter   adjusting the pH of the dispersion to a value between pH 3.5 and 4,   determining the zeta potential of the dispersion, and, if the zeta potential is negative,   further adjusting the pH of the dispersion to a value 0.5 above the previous pH value, and determining the zeta potential of the solution, and   repeating the adjustment step until a positive zeta potential is measured.   
     
     
         61 . The process according to  claim 60 , wherein the step of adjusting the pH of the dispersion to a value between 2 and 3.5 is performed by addition of HCl, and wherein both the step of adjusting the pH of the dispersion to a value between 3.5 and 4, and, if applicable, the steps of further adjusting the pH of the dispersion to a value 0.5 above the previous pH value, are performed by addition of NaOH. 
     
     
         62 . A process for preparing the negative electrode material according to  claim 40 , comprising:
 providing a nanosized silicon material, and   subjecting the silicon material to an atomic layer deposition process in a reaction chamber under a vacuum of at least 1 mbar and at a temperature between 50 and 500° C., making use of a gaseous organo-aluminum, organo-zinc or organo-antimony stream and water vapour, until a layer with a thickness between 2 and 10 nm is formed on the surface of the silicon material.   
     
     
         63 . The process according to  claim 62 , wherein the organo-aluminum compound is trimethyl aluminum. 
     
     
         64 . A process for preparing the negative electrode material according to  claim 49 , comprising:
 providing a nanosized silicon material, and dispersing the silicon material in water,   providing a quantity of cationic multivalent metal ions in the dispersion,   mixing the dispersion whereby the silicon material is at least partly covered by adsorbed cationic multivalent metal ions, and   drying the metal ion-silicon mixture.   
     
     
         65 . The process according to  claim 64 , further comprising:
 redispersing the dry metal ion-silicon mixture in water, and   acidifying the dispersion to a pH between 2 and 6.   
     
     
         66 . The process according to  claim 64 , wherein the metal ions are selected from the group consisting of Al-, Sb-, Fe-, Ti-, Zn-ions and combinations thereof. 
     
     
         67 . A process for preparing the negative electrode material according to  claim 51 , comprising:
 providing a nanosized silicon material,   dispersing the silicon material in water comprising ammonium ions, whereby the surface of the silicon material is at least partially covered with silanol groups,   providing an amino-functional metal oxide compound to the dispersion mixture,   agitating the mixture, whereby the silanol groups are covalently bound to the amino-functional metal compounds, and   drying the mixture.   
     
     
         68 . The process according to  claim 67 , wherein the metal oxide compound is selected from the group consisting of Si, Al and Ti and combinations thereof. 
     
     
         69 . A process for preparing the negative electrode material of  claim 52 , comprising:
 providing a nanosized silicon material,   dispersing the silicon material in water,   adding a quantity of nanoparticles of cationic multivalent metal oxides to the dispersion,   agitating the dispersion whereby the surface of the silicon material is at least partly covered by adsorbed nanoparticles of cationic multivalent metal oxides, and   drying the metal oxide-silicon mixture.   
     
     
         70 . The process according to  claim 69 , wherein the metal oxides are selected from the group consisting of Al-oxide, Ca-oxide, Mg-oxide, Pb-oxide, Sb-oxide, Fe-oxide, Ti-oxide, Zn-oxide, In-hydroxide and combinations thereof. 
     
     
         71 . The process according to  claim 60 , wherein the silicon material comprises either particles or a mixture of particles and wires, wherein both the particles and the wires are nano-sized, and wherein the average particle size of the particles is at least 5 times the average width of the wires. 
     
     
         72 . The process according to  claim 60 , wherein the silicon material comprises either
 pure silicon; or   a silicon monoxide powder, which comprises a mixture at nanometric scale of Si and SiO 2 ; or   silicon having a SiO x  surface layer, with 0<x<2, the surface layer having an average thickness between 0.5 nm and 10 nm; or   a homogeneous mixture of silicon- and metal-oxides, having the formula SiO x .(M a O b ) y , with 0<x<1 and 0≦y<1, wherein a and b are selected to provide electroneutrality, and wherein M is selected from the group consisting of Ca, Mg, Li, Al, Zn and combinations thereof; or   an alloy Si—X, wherein X is one or more metals selected from the group consisting of Sn, Ti, Fe, Ni, Cu, Co and Al.   
     
     
         73 . A process for preparing an electrode assembly for a rechargeable Li-ion battery comprising the negative electrode material according to  claim 40 , comprising:
 dispersing the negative electrode material according to  claim 40  in an aqueous solution, thereby obtaining a first slurry,   adjusting the pH of the first slurry to a value in the interval where the zeta potential of the negative electrode material is positive,   dissolving a CMC salt in water so as to obtain an aqueous solution of binder material,   adjusting the pH of the aqueous solution of binder material to a value in the interval where the zeta potential of the negative electrode material is positive,   mixing the first slurry and the aqueous solution of binder material to obtain a second slurry,   dispersing conductive carbon in the second slurry,   spreading the second slurry on a current collector, and   curing the electrode assembly comprising the second slurry at a temperature between 105 and 175° C.   
     
     
         74 . The process for preparing an electrode assembly according to  claim 73 , wherein the aqueous solution of binder material has a concentration of 1-4 wt % of Na-CMC.