Rechargeable batteries and methods of making same

Abstract

Systems and methods for rechargeable batteries are provided. In an embodiment, a battery may include a cathode, an anode, an electrolyte solution, and a current collector. The anode may include a 3D porous structure. The 3D porous structure may have a higher electrical conductivity at one end than at the other end, and lithium ions may be dispersed throughout the 3D porous structure.

Claims

1. An anode, comprising: an electrically conductive first layer comprising: a porous, three dimensional structure having a first end and a second end; a polymer; and particles comprising at least one of carbon and metal, said particles comprising a subset of particles, said subset having a high electrical conductivity that are distributed at a higher concentration toward the first end than the second end; and a second layer comprising a lithium metal, wherein the second layer is coupled to the first end of the first layer; wherein the particles satisfy at least one of the following (a) and (b): (a) the particles comprise at least one of copper and nickel, and are surface coated with at least one of tin, zinc, argon, bismuth, indium, gallium, aluminum, nitrogen, phosphorous, silicon, and germanium; and (b) the particles are doped with at least one of tin, zinc, argon, bismuth, indium, gallium, aluminum, nitrogen, phosphorous, silicon, and germanium.

2. The anode of claim 1, wherein the second end is configured to couple with a separator and an electrolyte solution.

3. The anode of claim 1, further comprising a metal current collector, wherein the current collector comprises at least one of copper, nickel, and stainless steel.

4. The anode of claim 2, further comprising a metal current collector, wherein the current collector comprises at least one of copper, nickel, and stainless steel.

5. The anode of claim 4, wherein the second layer comprises pure metallic lithium.

6. The anode of claim 2, wherein the first layer comprises a porosity between 60 and 90 percent.

7. The anode of claim 1, further comprising a third layer, the third layer being a metal current collector comprising at least one of copper, nickel, and stainless steel, and wherein the third layer is coupled to the second layer.

8. A battery, comprising: an anode, comprising: an electrically conductive first layer comprising: a porous, three-dimensional structure having a first end and a second end; a polymer; and particles comprising at least one of carbon and metal, said particles comprising a subset of particles, said subset having a high electrical conductivity that are distributed at a higher concentration toward the first end than the second end; and a second layer comprising lithium metal, wherein the second layer is coupled to the first end of the first layer wherein the particles satisfy at least one of the following (a) and (b): (a) the particles comprise at least one of copper and nickel, and are surface coated with at least one of tin, zinc, argon, bismuth, indium, gallium, aluminum, nitrogen, phosphorous, silicon, and germanium; and (b) the particles are doped with at least one of tin, zinc, argon, bismuth, indium, gallium, aluminum, nitrogen, phosphorous, silicon, and germanium.

9. The battery of claim 8, further comprising a metal current collector coupled to the second layer of the anode, wherein the current collector comprises at least one of copper, nickel, and stainless steel.

10. The battery of claim 8, further comprising a third layer of metal current collector coupled to the second layer of the anode, wherein the current collector comprises at least one of copper, nickel, and stainless steel.

11. The battery of claim 8, wherein the second layer of the anode comprises pure metallic lithium.

12. The battery of claim 8, wherein the first layer of the anode comprises a porosity between 60 percent and 90 percent.

13. The battery of claim 8, wherein the anode is further comprised of a third layer, the third layer being a metal current collector coupled to the second layer, and wherein the current collector comprises at least one of copper, nickel, and stainless steel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a set of diagrams depicting a prior art lithium anode;

(2) FIG. 2 is a schematic illustration of a 3D lithium anode, in accordance with various embodiments;

(3) FIG. 3 is a schematic illustration of a 3D lithium anode, in accordance with various embodiments;

DETAILED DESCRIPTION

(4) FIG. 2 is a schematic illustration of a 3D lithium anode, in accordance with various embodiments. In one embodiment, a 3D lithium anode 200 is coupled to an aqueous electrolyte solution 202 and may include a 3D conductive porous structure 204, a lithium metal layer 206, and a thin metal current collector 208. Current collector 208 may include a conventional anode current collector, including, but not limited to, copper, copper alloy, nickel, nickel alloy, stainless steel with thickness from 1 μm to 200 μm and more preferably, 5 μm to 10 μm. Lithium metal layer 206 may be made of pure metallic lithium with a thickness ranging from 5 μm to 200 μm. Lithium may be laminated or extruded on current collector 208 by any method known in the art. 3D porous structure 204 may have a thickness ranging from 5 μm to 500 μm, and more preferably from 10 μm to 150 μm, and most preferably from 20 μm to 80 μm.

(5) In an embodiment, 3D structure 204 may have a porosity ranging from 30% to 95%, and more preferably from 60% to 90%. 3D structure 204 may be made of conductive materials in the form of particles or fibers or any other shapes, and polymer binders, including but not limited to PVdF, or polyimide. The electronic conductivity of 3D structure 204 may be designed to have high electronic conductivity at the bottom of the layer and lower electronic conductivity at the top of the layer by adjusting the conductivity of the material compositions. The conductive materials used may include conductive carbon and conductive metals (such as copper, nickel). By varying the ratio of carbon and metal in the formula, the conductivity of 3D structure 204 can form a gradient since metals have higher specific conductivity than carbon. Further, carbon and metals can be coated or doped with other lithiophilic elements, including but not limited to Sn, Zn, Ag, Bi, In, Ga, Al, N, P, Si, Ge, or alloys of these elements. In preparation of 3D structure 204, conductive materials, polymer binder solution and/or pore former may be mixed to form a coating slurry, which may subsequently be casted on a substrate such as glass or release liner, followed by drying and removing of pore former and perhaps calendaring. A stand-alone 3D layer may thus be made. Such 3D structure 204 may be laminated onto metal/Li layer 206 or simply placed on top of the lithium layer 206 to make the 3D lithium anode for rechargeable lithium metal batteries.

(6) FIG. 3 is a schematic diagram of a 3D lithium anode, in accordance with various embodiments of the invention. In contrast to the anode shown in FIG. 2, the anode of FIG. 3 may lack a thin metal current collector, but may otherwise include all other structures as shown in FIG. 2.

(7) Due to the conductivity gradient, different from any other 3D lithium anode, the lithium deposition may start from the bottom to top, instead of from the top to the bottom. The lithium stripping during cell discharging may thus start from the top to the bottom. This process may thus prevent lithium dendrite growth on top of 3D current collector. Moreover, doping and coating with lithiophilic elements can facilitate the smooth growth of lithium on top of 3D layer.

(8) Unlike in the thermal lithium infusion method and the electrochemical plating method, in this method lithium foil can provide the lithium source.

Example 1. Zinc Doped Copper Powder

(9) In an embodiment, a method of forming a lithium anode may be provided. In accordance with various embodiments, a brass powder with particle size about 10 μm to 50 μm was first washed with dehydrated alcohol to remove surface impurities. Then the powder was immersed in 1 M HCl and 2 M ammonium chloride water solution at elevated temperature of 50° C. After a couple of hours, the powder color changed from golden color to copper color. The power was then filtered and rinsed with copious water, followed by drying in the oven. The collected powder can be used directly to make the 3D structure or can be ball milled to reduce the size of the particle. By controlling the etching time, the residual amount of Zinc in the powder can be adjusted. The lithiophilic zinc can facilitate the uniform lithium deposition on 3D substrate.

(10) In another embodiment, porous copper powder may be produced with well-established methods by etching of Zn or Mn from brass alloy or CuMn alloy powders. With controlled alloy composition and etching condition, nanoporous copper with different pore sizes can be made (as shown in FIG. 2a). After ball milling, 5˜10 um size copper powder with submicron pores can be obtained. Such porous copper powder along with binder may be mixed and coated on the copper foil followed by drying, additional porous carbon layer coating, drying and calendaring. 3D current collector can thus be made with conventional coating process. In order to improve the lithiophilicity, residual zinc in copper through incomplete etching of brass will be used in this embodiment.

Example 2. Evaporation of Zinc on Nickel Powders

(11) Nickel filament powder T255 from Vale with primary particle size of 2.2˜2.6 μm can be surface coated with thermal evaporation processes as follows:

(12) Mix 2 gram of metallic zinc flake and 1 gram of activated carbon in a ceramic boat.

(13) Evenly spread 10 grams of nickel powders (Novamet Ni 255) on a pressed Ni sponge.

(14) Place the Ni sponge on the mixed zinc flake and activated carbon.

(15) Cover Ni powders with another Ni sponge.

(16) Insert the ceramic boat into the center of a quartz tube inside the tubular oven.

(17) Flush the quartz tube with forming gas (5 vol. % H.sub.2 in N.sub.2) for 10 minutes.

(18) Increase temperature to 600° C.˜700° C. at a rate of 5° C. per minute.

(19) Keep the desired temperature for up to 30 minutes.

(20) Cool down to room temperature.

(21) The weight percentage of zinc on nickel powders are about 5 wt % to 15 wt %, depending on the annealing temperature and time.

(22) The zinc coated Ni powder was then employed to make the 3D structure.

Example 3. Zinc Coated Nickel Powder

(23) Sol-Gel coating process can also be used to coat the zinc oxide surface layer on nickel particles, followed by thermal reduction in forming gas, specifically:

(24) Prepare Zn-containing sol solution in a 100 mL glass beaker by mixing zinc precursor (zinc acetate or zinc nitrate) and base (butylamine or ammonium hydroxide or mixed) in organic solvent (ethanol or 2-propanol).

(25) Stir the sol solution for up to 5 hours at a mild temperature of 60-70° C.

(26) Add 10.0 grams Ni powders (Novamet, Ni 255) into the sol solution.

(27) Stir the mixed dispersion in a hood for more than 8 hours, until the completely evaporation of the organic solvent.

(28) Transfer the Zn-precursor coated Ni powders into a ceramic boat and insert it into the center of a quartz tube inside the tubular oven.

(29) Flush the quartz tube with forming gas (5 vol. % H.sub.2 in N.sub.2) for 10 minutes.

(30) Increase temperature to 80° C. at a rate of 2° C. per minute and then keep the temperature for 4 hours.

(31) Increase temperature to 550-650° C. at a rate of 1° C. per minute and then keep the temperature for up to 30 minutes.

(32) Cool down to room temperature.

(33) The weight percentage of zinc on nickel powders are about 5 wt % to 15 wt %, depending on the ratio of Zn precursor, final annealing temperature and time.

(34) Zinc coated nickel powder thus made can be used to make 3D conductive structure for lithium anode.

Example 4. Doped Carbon Black

(35) Zinc doped carbon black was prepared according to the following procedures:

(36) Carbon black is soaked in zinc nitrate solution in weight ratio of 95:5.

(37) Solution is dried.

(38) Dry powder is heated up in tube furnace under flow of forming gas at 320° C. to decompose zinc nitrate for 1 hour; The temperature is then ramped up to 600° C. and kept at 600° C. for 2 hours.

(39) After cooling down, zinc doped carbon black can be obtained.

(40) The method of making nitrogen doped carbon black is well known in the art.

Example 5. 3D Structured Porous Nickel Film

(41) Porous 3D structure can be made by following procedures:

(42) Make 10% Matrimid solution by adding 1.02 g (Matrimid 5218, Huntsman) in a 4-ounce plastic container with 9.01 g NMP (1-methyl-2-pyrrolidinone, 99.5% Sigma-Aldrich) under vigorous stirring, at room temperature overnight.

(43) Make precursor by adding 4.0 gram Zn-coated Ni powder (Ni 255 coated with Zn) in the above container with 10.0 gram 10% Matrimid solution.

(44) Mix the precursor with centrifuge mixer (Speed Mixer, DAC 150 FVZ) at 2700 rpm for 2 min, three times.

(45) Cast the precursor on clean glass plate with 5 and 10 mil casting blade, respectively

(46) Then place the glass plates in a hood for 4-6 hour at room temperature

(47) Merge the plates into warm water (40-50° C.), and gently peel off the films from the glass plate.

(48) Dry the films for 1 day at room temperature

(49) The thickness of the films are 33 μm, 55 μm, respectively

(50) The thickness of the film can be varied by changing the gap of doctor blade. Other polymer resins, including but not limited to polyamide, polyamide imide, polyvinylidene fluoride, polyether ether ketone, can also be used to replace Matrimid. Pore former can also be included to change the porosity of the film.

Example 6. 3D Structure with Conductivity Gradient

(51) Similar to Example 5, mixed N-doped carbon black and Zn coated nickel power were employed along with polymer binder. A thin layer with high percentage of zinc coated nickel powder was casted and dried, which was followed by additional casting with formula containing high percentage of N-doped carbon (lower electronic conductivity). After peeling off and drying, 3D structured porous film with conductivity gradient can be made. The layer with high metal content and higher conductivity will be placed directly on top of lithium metal foil or lithium metal foil on copper current collector to make 3D lithium anode.

(52) Similar to Example 5, mixed N-doped carbon black and Zn doped copper (made from Example 1) were employed along with polymer binder. A thin layer with high percentage of Zn doped copper powder was first casted, followed by a layer of coating with high percentage of N-doped carbon black. After peeling off and drying, 3D structured porous copper film with conductivity gradient can be made. 3D lithium anode can be made similarly.

Example 7. Porosity Control of 3D Structure

(53) Similar to the process used in example 5, additional microsize NaCl salt was added in certain percentage to make the casting slurry. After milling, the homogeneous ink will be used to cast the 3D structured substrate. After drying and peeling off, the film is then soaked in distilled water for a period of time, followed by drying in vacuum oven. By controlling the amount of NaCl addition (as pore former), the film porosity can be controlled to up to 95%.

Example 8. 3D Lithium Anode

(54) 3D lithium anode was made by laminating a layer of 3D structure made in Example 6 on top of lithium foil. This 3D lithium anode was punched in a disk size. Symmetric cells (cell type A) were made with two pieces of 3D lithium anode with Celgard 2400 separator and 1M LiPF.sub.6 in DMC/EC (1:1) electrolyte. The cells were charged and discharged at 0.5 mA/cm.sup.2 for 2 hours. As comparison, symmetric cells (cell type B) were made with two pieces of metallic lithium disk with Celgard 2400 separator and 1M LiPF.sub.6 in DMC/EC (1:1) electrolyte and were cycled at 0.5 mA/cm.sup.2 for 2 hours. The cell type A can last over a few hundred cycles before exhibiting increasing of cell voltage, while cell type B can only last for less than 15 cycles before cells develop erratic voltage profiles. Cell type A can also be cycled stably at high current density of 10 mA/cm.sup.2 while cell type B cannot be cycled at such high current density for more than 10 cycles.

(55) 3D lithium anode with 3D structure with conductivity gradient can not only facilitate the bottom-up lithium deposition, but also block the lithium dendrite growth—extending the cycle life lithium metal batteries.

Example 9. Rechargeable Lithium Metal Cells

(56) 3D structure with conductivity gradient was made with Zn doped copper powder and N-doped carbon black. 3D lithium anode can then be made by laminating this 3D film on top of lithium metal or lithium metal on copper current collector. Disk of 3D lithium anode can be punched out. Coin cells can be made with NMC 532 cathode, Celgard 2400 separator and 3D lithium anode. Conventional electrolyte or any proper non-aqueous electrolyte can be used to make the coin cell. The cell was then be charged and discharged at C/5, C/2 and 5 C rate. Conventional coin cells with conventional lithium foil anode were also fabricated and cycled. The cells with 3D lithium anode showed much longer cycle life and higher rate capability than the conventional cells.