Battery electrode structure and method for manufacture thereof

Abstract

There are disclosed solid composite electrodes with electrode active layers that include an electrode active material, an optional election conductive material, an optional binder and other optional additives. The solid composite electrodes are formed by the deposition of an electrode composition (slurry) onto a current collector in one or many layers. The electrode structure may be characterised by a porosity of the electrode composition layer that decreases in a direction from the back side of the layer (close to the current collector) towards the outer side of the layer. The gradient of the decrease in the porosity is controlled by the content of solid substance in the slurry, by the composition of the solvent in the slurry, by the temperature of the layer drying after deposition, as well as by the pressing or calendering conditions for each layer. The electrode structures can be used in for example chemical sources of electric energy such as primary (non-rechargeable) as well as secondary (rechargeable) batteries.

1 . An electrode structure for a chemical source of electric energy, the electrode structure comprising at least a current collector and an electrode composition provided on the current collector, wherein 
 a) said electrode composition includes an electrochemically active material;    b) said electrode composition is provided on the current collector in one or several layers and has an inside surface proximal to the current collector and an outside surface distal from the current collector; and    c) said electrode composition has a non-uniform porosity that decreases in a direction from the inside surface towards the outside surface.    
   
   
       2 . An electrode structure as claimed in  claim 1 , configured as a positive electrode.  
   
   
       3 . An electrode structure as claimed in  claim 2 , wherein the electrochemically active material is selected from a list comprising: sulphur, non-organic and organic (including oligomeric and polymeric) compounds based on sulphur, simple and complex metal oxides, sulphides and mixtures thereof.  
   
   
       4 . An electrode structure as claimed in  claim 1 , configured as a negative electrode.  
   
   
       5 . An electrode structure as claimed in  claim 4 , wherein the electrochemically active material is selected from a list comprising: metal powders, alkali metal-carbon and alkali metal-graphite intercalates and mixtures thereof.  
   
   
       6 . An electrode structure as claimed in  claim 1 , wherein the electrode composition further includes a binder.  
   
   
       7 . An electrode structure as claimed in  claim 1 , wherein the electrode composition further includes an electron conductive material.  
   
   
       8 . An electrode structure as claimed in  claim 1 , wherein the electrochemically active material constitutes 5% to 95% by weight of the electrode composition.  
   
   
       9 . An electrode structure as claimed in  claim 1 , wherein the electrochemically active material constitutes at least 70% by weight of the electrode composition.  
   
   
       10 . An electrode structure as claimed in  claim 7 , wherein the electron conductive material constitutes up to 70% by weight of the electrode composition.  
   
   
       11 . An electrode structure as claimed in  claim 7 , wherein the electron conductive material is selected from a list comprising: conductive polymers, carbon fibres, metal fibres, carbon powders, metal powders, carbon flakes and metal flakes.  
   
   
       12 . An electrode structure as claimed in  claim 11 , wherein the carbon powder is selected from a list comprising: soot and carbon black.  
   
   
       13 . An electrode structure as claimed in  claim 6 , wherein the binder is selected from a list of polymers comprising: polyethylene oxides, polypropylene oxides, polyacrylonitriles, polysiloxanes, polyimides, polyphosphazenes, polyethers, sulfonated polyimides, perfluorinated polymers, polydivinyl polyethylene glycols, polyethylene glycol diacrylates, polyethylene glycol dimethacrylates, polyarylsulfones, mixtures and derivatives of said polymers, and copolymers that include repeating units of said polymers.  
   
   
       14 . An electrode structure as claimed in  claim 6 , wherein the binder comprises 0.5% to 30% by weight of the electrode composition.  
   
   
       15 . An electrode structure as claimed in  claim 1 , wherein the electrode composition is present as a single layer.  
   
   
       16 . An electrode structure as claimed in  claim 1 , wherein the electrode composition is present as multiple layers.  
   
   
       17 . An electrode structure as claimed in  claim 15 , wherein the layer has a thickness of 0.1 to 10 μm.  
   
   
       18 . An electrode structure as claimed in  claim 16 , wherein the electrode composition is present as 1 to 10 layers.  
   
   
       19 . An electrode structure as claimed in  claim 16 , wherein the layers have a total thickness of to 100 μm.  
   
   
       20 . An electrode structure as claimed in  claim 1 , wherein the electrode composition has an average porosity of 5% to 85%.  
   
   
       21 . A method of producing an electrode structure for a chemical source of electric energy, the method comprising: 
 a) providing a current collector;    b) coating a layer or a plurality of successive layers of an electrode composition on the current collector so as to produce a coating having an inside surface proximal to the current collector and an outside surface distal from the current collector; and    c) using a coating process or post-treating the coating so that the coating has a non-uniform porosity that decreases in a direction from the inside surface towards the outside surface.    
   
   
       22 . A method according to  claim 21 , wherein the electrode composition includes an electrochemically active material selected from a list comprising: sulphur, non-organic and organic (including oligomeric and polymeric) compounds based on sulphur, simple and complex metal oxides, sulphides and mixtures thereof.  
   
   
       23 . A method according to  claim 21 , wherein the electrode composition includes an electrochemically active material selected from a list comprising: metal powders, alkali metal-carbon and alkali metal-graphite intercalates and mixtures thereof.  
   
   
       24 . A method according to  claim 21 , wherein the electrode composition further includes an electron conductive material.  
   
   
       25 . A method according to  claim 21 , wherein the electrode composition further includes a binder.  
   
   
       26 . A method according to  claim 24 , wherein the electron conductive material is selected from a list comprising: conductive polymers, carbon fibres, metal fibres, carbon powders, metal powders, carbon flakes and metal flakes.  
   
   
       27 . A method according to  claim 26 , wherein the carbon powder is selected from a list comprising: soot and carbon black.  
   
   
       28 . A method according to  claim 25 , wherein the binder is selected from a list of polymers comprising: polyethylene oxides, polypropylene oxides, polyacrylonitriles, polysiloxanes, polyimides, polyphosphazenes, polyethers, sulfonated polyimides, perfluorinated polymers, polydivinyl polyethylene glycols, polyethylene glycol diacrylates, polyethylene glycol dimethacrylates, mixtures and derivatives of said polymers, and copolymers that include repeating units of said polymers.  
   
   
       29 . A method according to  claim 21 , wherein the electrode composition is applied as a slurry.  
   
   
       30 . A method according to  claim 29 , wherein the slurry is prepared by grinding and homogenising the electrode composition and adding a solvent.  
   
   
       31 . A method according to  claim 30 , wherein the slurry comprises 5% to 50% by weight solids, the remainder being the solvent.  
   
   
       32 . A method according to  claim 29 , wherein a first, single coating of slurry is applied to the current collector and allowed to dry.  
   
   
       33 . A method according to  claim 32 , wherein further coatings of slurry are applied after the first coating has been allowed to dry.  
   
   
       34 . A method according to  claim 21 , wherein each layer is compressed or calendered after application to the current collector.  
   
   
       35 . A method according to  claim 33 , wherein successive coatings are applied with different slurry compositions.  
   
   
       36 . A method according to  claim 35 , wherein the slurry compositions have different solids to solvent ratios.  
   
   
       37 . A method according to  claim 33 , wherein successive coatings are allowed to dry under different temperature or pressure conditions.  
   
   
       38 . A method according to  claim 33 , wherein successive coatings ate compressed or calendered under different conditions.  
   
   
       39 . A battery made by the method of  claim 21 .  
   
   
       40 . A battery including at least one electrode structure as claimed in  claim 1 .  
   
   
       41 . A battery as claimed in  claim 40 , wherein the battery is a lithium battery or a lithium-ion battery.  
   
   
       42 . A battery as claimed in  claim 40 , wherein the battery is a lithium polymer battery.  
   
   
       43 . A battery as claimed in  claim 40 , wherein the battery has an operating voltage of 1.2 to 4.1V.