Separator for electrochemical cell and method for its manufacture

An electrode/separator assembly for use in an electrochemical cell, comprising:

• a current collector;
• a porous composite electrode layer adhered to the current collector, said electrode layer comprising at least electroactive particles and a binder;
• and
• a porous composite separator layer comprising inorganic particles substantially uniformly distributed in a polymer matrix to form nanopores and having a pore volume fraction of at least 25%, wherein the separator layer is secured to the electrode layer by a solvent weld at the interface between the two layers, said weld comprising a mixture of the binder and the polymer.

A method of preparing a electrode/separator assembly for an electrochemical cell, said method comprising:

• providing a porous composite electrode layer comprising at least electroactive particles and a binder;
• providing a coating solution, said coating solution comprising a polymer, solvent system for said polymer, and inorganic particles dispersed in said solvent, wherein said solvent system is selected to have at least some solubility for the binder of the electrode layer;
• coating a surface of said electrode layer with a layer of said coating solution, wherein the coating solution penetrates a fraction of the thickness of the electrode layer and dissolves a portion of the binder;
• and
• removing the solvent from said coating solution layer to deposit a porous separator layer comprising inorganic particles substantially uniformly distributed in the polymer and having a pore volume fraction of at least 25% and to form a solvent weld at an interface between said porous electrode layer and said porous separator layer.

A method of preparing a defect-free separator membrane where defects are defined as discontinuities which short the cell or permit unacceptably high leakage currents for an electrochemical cell, or otherwise reduce performance in cycling and pulsing the cell currents, said method comprising:

• providing a coating solution, said coating solution comprising a polymer having a melting temperature, a solvent for said polymer, and an inorganic material dispersed in said solvent;
• providing a support;
• coating a surface of said support with a plurality of layers of said coating solution with drying by heat after each deposition, each said layer depositing a portion of the final thickness;
• and
• subjecting the membrane with the desired thickness to a stress-relieving treatment, whereby a porous body comprised of said polymer and said inorganic is deposited on said surface of said electrode, said body comprising being substantially free of cracks and other defects.

A laminate electrochemical cell, comprising:

• a stack of layers arranged to provides a positive electrode layer/separator layer/negative electrode layer/separator layer repeat unit, where:
• the positive electrode layer comprises a porous composite positive electrode layer adhered to both sides of a positive current collector, said electrode layer comprising at least electroactive particles and a binder;
• the negative electrode layer comprises a porous composite negative electrode layer adhered to a both sides of a negative current collector, said electrode layer comprising at least electroactive particles and a binder;
• the separator layer comprises a porous composite separator layer comprising inorganic particles substantially uniformly distributed in a polymer matrix to form nanopores,
• wherein each separator layer is bonded to an adjacent electrode layer through a solvent weld at an interface between the separator layer and the electrode layer.

A method of making a laminate electrochemical cell, comprising:

• providing stacked cell units comprising a plurality of positive electrode layer/separator layer/negative electrode layer/separator layer repeat units, where:
• the positive electrode layer comprises a porous composite positive electrode layer adhered to both sides of a positive current collector, said electrode layer comprising at least electroactive particles and a binder;
• the negative electrode layer comprises a porous composite negative electrode layer adhered to a both sides of a negative current collector, said electrode layer comprising at least electroactive particles and a binder;
• the separator layer comprises a porous composite separator layer comprising inorganic particles substantially uniformly distributed in a polymer matrix to form nanopores;
• and
• applying heat and/or pressure to the stacked cell units to soften the binder and polymer of the electrode and separator layers and fuse adjacent separator and electrode layers to form a solvent weld.