Integral bi-layer separator-electrode construction for lithium-ion batteries

Abstract

A porous bi-layer separator composed of a first layer with a contacting array of non-conducting particles overlaid with a second layer of a microporous polymer layer, may be fabricated on the electrode surface of the anode of a lithium-ion battery to form an integral electrode-separator construction. The bi-layer separator may prevent development of a direct electronic path between the anode and cathode of the battery while accommodating electrolyte solution and enabling passage of lithium ions. Such an integral separator should be mechanically robust and tolerant of elevated temperatures. Exemplary bi-layer separators may be fabricated by sequential deposition of solvent-containing slurries and polymer solutions with subsequent controlled evaporation of solvent. The elevated temperature performance of lithium-ion battery cells incorporating such integral electrode-bi-layer separators was demonstrated to exceed the performance of similar cells using commercial and experimental single layer polymer separators.

1 . A cell for a lithium-ion battery, the cell comprising, as thin layers, stacked cell components consisting essentially of:
 an elemental lithium-containing anode layer having an anode face and an anode peripheral shape and being carried on an anode current collector;   a lithium ion-accepting cathode layer, having a cathode face and a cathode peripheral shape and carried on a cathode current collector, the faces of the anode and cathode facing each other;   a liquid lithium ion electrolyte for transport of lithium ions between the layer surfaces of the anode and cathode; and   a bi-layer separator, with a peripheral shape, integrally formed on, and attached to, one of the anode and cathode layers so as to separate their respective faces, the total thickness of the cell components being up to about one millimeter;   the separator comprising;   a tiered layer of substantially-equiaxed, electrically non-conductive particles of an average size lying on the layer surface of one of the anode or cathode, within its peripheral shape, and providing many non-straight porous paths through the thickness of the layer of particles, the thickness of the layer being at least equivalent to twice the average sizes of the particles; and   a layer of a polymer containing pores for infiltration of the electrolyte through the polymer layer and through the tiered layer of particles for transport of lithium ions between the opposing faces of the electrodes;   the thickness of the layer of particles and the polymer layer cooperating to prevent penetration of the bi-layer by an electrically-conducting body extending from the anode surface to the cathode surface to form a short-circuit path in the cell.   
     
     
         2 . A lithium-ion battery as recited in  claim 1  in which the ion-transporting polymer layer is formed by phase separation from a liquid mixture comprising the polymer, a polymer solvent and a polymer non-solvent. 
     
     
         3 . A lithium-ion battery as recited in  claim 1  in which the ion-transporting polymer layer is formed by phase separation from a liquid mixture comprising polyvinylidene fluoride (PVDF), acetone and water. 
     
     
         4 . A lithium-ion battery as recited in  claim 1  in which the electrically non-conducting particles are oxides or nitrides of one or more of the group consisting of silicon, aluminum, titanium, magnesium or calcium. 
     
     
         5 . A lithium-ion battery as recited in  claim 1  in which the electrically non-conducting particles are bound to one another and to the anode or cathode on which they lie. 
     
     
         6 . A lithium-ion battery as recited in  claim 1  in which the average particle size ranges from about 0.005 micrometers to 10 micrometers. 
     
     
         7 . A lithium-ion battery as recited in  claim 1  in which the thickness of the particle layer ranges from about 5 micrometers to about 40 micrometers. 
     
     
         8 . A lithium-ion battery as recited in  claim 1  in which the anode peripheral shape is greater than the cathode peripheral shape and the bi-layer peripheral shape is at least as great as the anode peripheral shape. 
     
     
         9 . A lithium-ion cell with a lithium-ion electrolyte, an anode and a cathode, each of the anode and cathode having a face, and each of the anode and cathode arranged with their faces in opposition, the anode face having an integral bi-layer separator;
 the bi-layer separator comprising a particle layer in contact with the anode face and a polymer layer;   the particle layer comprising an array of abutting electrically non-conducting particles with an average particle size and a plurality of tortuous pores extending through the layer;   the polymer layer having a thickness and opposing sides, one side being attached to the anode and at least coextensive with, and overlying the particle layer to maintain the particle layer in contact with the anode   
     
     
         10 . An anode for a lithium-ion battery as recited in  claim 9  in which the electrically non-conducting particles are oxides or nitrides of one or more of the group consisting of silicon, aluminum, titanium, magnesium or calcium. 
     
     
         11 . An anode for a lithium-ion battery as recited in  claim 9  in which the particles of the particle layer are attached to each other and the particle layer is attached to the anode surface by a binder. 
     
     
         12 . An anode for a lithium-ion battery as recited in  claim 9  in which the average particle size is less than one-half of the thickness of the particle layer. 
     
     
         13 . An anode for a lithium-ion battery as recited in  claim 9  in which the average particle size ranges from about 0.005 micrometers to 10 micrometers. 
     
     
         14 . An anode for a lithium-ion battery as recited in  claim 9  in which the polymer layer comprises open pores that interconnect the sides of the layer for accommodation of the lithium-ion electrolyte and transport of lithium ions, the open-pored polymer layer being formed by phase separation from a liquid mixture comprising the polymer, a polymer solvent and a polymer non-solvent. 
     
     
         15 . An anode for a lithium-ion battery as recited in  claim 9  in which the polymer of the polymer layer comprises polyvinylidene fluoride (PVDF) with open pores that interconnect the sides of the layer for accommodation of the lithium-ion electrolyte and transport of lithium ions, the open-pored PVDF layer being formed by phase separation from a liquid mixture comprising PVDF, acetone and water. 
     
     
         16 . An anode for a lithium-ion battery as recited in  claim 9  in which the polymer of the polymer layer is poly(methyl methacrylate) PMMA formed by evaporation of PMMA-solvent solution to form a continuous layer of PMMA which, when immersed in the lithium-ion conducting electrolyte, forms a lithium-ion conducting gel for transport of lithium ions. 
     
     
         17 . A method of making an anode with an integral bi-layer separator for a lithium-ion battery, the bi-layer separator comprising a particle layer and a polymer layer and being adapted for transport of lithium ions to and from the anode while preventing passage of electrons when immersed in a liquid electrolyte, the method comprising:
 spreading a slurry of graphite, carbon black and a first binder dissolved in a first solvent on a copper current collector and evaporating the solvent to form an anode with a first surface in contact with the current collector and a carbonaceous surface;   forming the particle layer of the bi-layer separator by:   spreading a slurry of electrically non-conducting particles in a solution of a second binder and a second solvent on the carbonaceous surface of the anode to form a layer of generally uniform thickness on the anode;   partially or completely evaporating the second solvent to form a particle layer of the bi-layer separator, the particle layer comprising a plurality of abutting particles with pores extending throughout the layer, the layer having two opposing surfaces, an anode surface in contact with the anode and a particulate surface; then   forming the polymer layer of the bi-layer separator by;   applying a generally uniform thickness of a solution comprising a polymer dissolved in a third solvent to the particulate surface of the particle layer;   evaporating the third solvent to form the polymer layer overlying, and adhering to, the particle layer, the polymer layer being adapted for transport of ions through the polymer when immersed in a liquid electrolyte.   
     
     
         18 . A method of making an anode with an integral bi-layer separator for a lithium-ion battery as recited in  claim 16  in which the polymer layer is formed by applying a substantially uniform layer of a polymer solution dissolved in an solution comprising a polymer solvent and a polymer non-solvent; then
 selectively evaporating the polymer solvent at a temperature suitable for forming a phase-separated non-solvent and polymer mixture and then evaporating the non-solvent to form a microporous polymer layer in which pores extend from a first particulate-contacting surface of the polymer layer to a second opposing surface of the layer are adapted to be filled with liquid electrolyte for transport of lithium ions. 
 
     
     
         19 . A method of making an anode with an integral bi-layer separator for a lithium-ion battery as recited in  claim 16  in which the polymer is polyvinylidene fluoride (PVDF), the polymer solvent is acetone and the polymer non-solvent is water. 
     
     
         20 . A method of making an anode with an integral bi-layer separator for a lithium-ion battery as recited in  claim 16  in which the polymer layer is formed by applying a substantially uniform layer of a poly(methyl methacrylate) (PMMA) solution dissolved in an acetone solvent; then
 evaporating the acetone to form a PMMA layer adapted to form a lithium-ion conducting gel when immersed in liquid electrolyte.