Process for lithiating negative electrodes for lithium ion electrochemical cells
Methods for pre-lithiating negative electrodes for lithium-ion electrochemical cells (e.g., batteries) are provided. The methods include disposing a lithium metal source comprising a layer of lithium metal adjacent to a surface of a pre-fabricated negative electrode. The lithium metal source and electrode are heated (e.g., to a temperature of ≧about 100° C.) to transfer a quantity of lithium to the pre-fabricated negative electrode. This lithiation process adds excess active lithium capacity that enables replacement of irreversibly lost lithium during cell formation and cell aging, thus leading to increased battery capacity and improved battery life. The methods may be batch or continuous.
1. A method of making a pre-lithiated negative electrode for a lithium-ion electrochemical cell, the method comprising:
disposing a lithium metal source comprising a layer of lithium metal adjacent to a surface of a pre-fabricated negative electrode;
heating and compressing the lithium metal source and the pre-fabricated negative electrode together to a temperature of greater than or equal to about 115° C. to less than or equal to about 175° C. and applying pressure at greater than or equal to about 10 MPa to less than or equal to about 30 MPa for greater than or equal to about 15 minutes to transfer a quantity of lithium to the pre-fabricated negative electrode, wherein the quantity of lithium transferred per area of the pre-fabricated negative electrode is greater than or equal to about 0.01 mg/cm 2 to less than or equal to about 1 mg/cm 2 ; and
separating the lithium metal source from the surface of the pre-fabricated negative electrode to form the pre-lithiated negative electrode.
2. The method of claim 1 , wherein the compressing occurs by first disposing the lithium metal source on a first plate and the pre-fabricated negative electrode on a second plate and applying pressure between the plates.
3. The method of claim 1 , wherein the method further comprises incorporating the pre-lithiated negative electrode into an electrochemical cell further comprising a positive electrode, a separator, and an electrolyte, wherein the electrochemical cell has an initial capacity of greater than or equal to about 16.5 Amp-hours to less than or equal to about 18 Amp-hours prior to a first charge and discharge cycle, wherein the quantity of lithium transferred to the pre-lithiated negative electrode is greater than or equal to about 1.5 Amp-hours to less than or equal to about 3 Amp-hours.
4. The method of claim 1 , wherein the quantity of lithium transferred per area of the pre-fabricated negative electrode is greater than or equal to about 0.05 mg/cm 2 to less than or equal to about 0.5 mg/cm 2 .
5. The method of claim 1 , wherein the lithium metal source further comprises a carrier substrate on which the layer of lithium metal is disposed.
6. The method of claim 5 , wherein the carrier substrate is selected from the group consisting of: fluoropolymers, copper foil, and nickel foil.
7. The method of claim 1 , wherein the layer of lithium metal comprises a lithium foil.
8. A continuous method of making a pre-lithiated negative electrode for a lithium-ion electrochemical cell, the method comprising:
conveying a first sheet comprising a pre-fabricated negative electrode material and a second sheet comprising a lithium metal layer and a carrier substrate layer together into a calendaring system, wherein the lithium metal layer contacts a surface of the pre-fabricated negative electrode material in the calendaring system;
applying heat and pressure to the first sheet and the second sheet to transfer lithium to the pre-fabricated negative electrode material to form a pre-lithiated negative electrode material wherein a temperature is greater than or equal to about 115° C. to less than or equal to about 175° C. and the pressure is greater than or equal to about 10 MPa to less than or equal to about 30 MPa, wherein a quantity of lithium transferred per area of the pre-fabricated negative electrode is greater than or equal to about 0.01 mg/cm 2 to less than or equal to about 1 mg/cm 2 ; and
separating the second sheet from the pre-lithiated negative electrode material.
9. The continuous method of claim 8 , further comprising sectioning the pre-lithiated negative electrode material after the separating to form a plurality of pre-lithiated electrodes.
10. The continuous method of claim 8 , wherein the method further comprises incorporating the pre-lithiated negative electrode into an electrochemical cell further comprising a positive electrode, a separator, and an electrolyte, wherein the electrochemical cell has an initial capacity of greater than or equal to about 16.5 Amp-hours to less than or equal to about 18 Amp-hours prior to a first charge and discharge cycle, wherein a quantity of lithium transferred to the pre-lithiated negative electrode is greater than or equal to about 1.5 Amp-hours to less than or equal to about 3 Amp-hours.
11. The continuous method of claim 8 , wherein a quantity of lithium transferred per unit area of the pre-fabricated negative electrode is greater than or equal to about 0.05 mg/cm 2 to less than or equal to about 0.5 mg/cm 2 .
12. The continuous method of claim 8 , wherein the carrier substrate is selected from the group consisting of: fluoropolymers, copper foil, and nickel foil.
13. The continuous method of claim 8 , wherein the lithium metal layer comprises a lithium foil.
14. A method of making a lithium-ion electrochemical cell, the method comprising:
disposing a lithium metal source comprising a layer of lithium metal adjacent to a surface of a pre-fabricated negative electrode;
heating and compressing the lithium metal source and the pre-fabricated negative electrode together at a temperature of greater than or equal to about 115° C. to less than or equal to about 175° C. and applying pressure at greater than or equal to about 10 MPa to less than or equal to about 30 MPa to transfer a quantity of lithium to the pre-fabricated negative electrode, wherein the quantity of lithium transferred per area of the pre-fabricated negative electrode is greater than or equal to about 0.01 mg/cm 2 to less than or equal to about 1 mg/cm 2 ;
separating the lithium metal source from the surface of the pre-fabricated negative electrode to form a pre-lithiated negative electrode; and
forming the lithium-ion electrochemical cell by assembling the pre-lithiated negative electrode with a negative current collector, a positive electrode and positive current collector, a separator, and an electrolyte, wherein the lithium-ion electrochemical cell has an initial capacity of greater than or equal to about 16.5 Amp-hours to less than or equal to about 18 Amp-hours prior to a first charge and discharge cycle, wherein the quantity of lithium transferred to the pre-lithiated negative electrode is greater than or equal to about 1.5 Amp-hours to less than or equal to about 3 Amp-hours.