Three-dimensional current collector for metal secondary battery anode, its preparation and application

Abstract

The present invention provides a three-dimensional current collector used in a metal secondary battery and the preparation method of said current collector. Said current collector is a three-dimensional porous hollow carbon fiber current collector which has both porous structure and hollow structure and is used to load metal anode, so that lithium dendrites growth can be suppressed and the Coulombic efficiency can be improved. Said current collector is intertwined by micrometer-sized hollow carbon fibers with the diameter of 1 to 50 μm, the wall thick of 0.5 to 6 μm, and the pore volume of 0.005 to 0.05 cm.sup.3 cm.sup.−2.

Claims

1. A method for preparing a three-dimensional porous current collector comprising a plurality of hollow carbon fibers, each hollow carbon fiber having a hollow center of a diameter of 3 to 20 μm for loading a metal anode and suppressing lithium dendrites growth, and a wall thickness of 1 to 3 μm, and the three-dimensional porous current collector has having an areal pore volume of 0.01 to 0.03 cm.sup.3/cm.sup.2, the method comprises the following steps: preparing a raw material made from cotton by washing, drying, rolling, and slicing; carbonizing the raw material by calcination in a protective atmosphere at 800 to 1200° C. for 30 minutes to 5 hours to obtain a carbonized material; activating the carbonized material in a protective atmosphere by first soaking in a series of activating agents selected from KOH and NaOH with a concentrations of 0.5 M-5 M; and then drying and calcining in the protective atmosphere at 400 to 900° C. at a heating rate of 1 to 10° C/min for 20 min to 6 h to obtain an activated material; washing the activated material, first with diluted hydrochloric acid or dilute sulfuric acid, then with deionized water and ethanol, and drying to obtain the plurality of hollow carbon fibers.

2. The method according to claim 1, wherein the raw material is one or more selected from cotton cloth, and medical absorbent cotton, and the protective atmosphere is inert gas selected from argon, helium, nitrogen, and mixtures thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a top view scanning electron microscope (SEM) image of the three-dimensional porous hollow carbon fibers obtained in embodiment 1 of the present invention.

(2) FIG. 2 is a cross-section view SEM image of the three-dimensional porous hollow carbon fibers obtained in embodiment 1 of the present invention.

(3) FIG. 3 is cross-sectional view SEM images of (FIG. 3 panel a) the pristine three-dimensional porous hollow carbon fibers and after plating (FIG. 3 panel b) 1 mA h cm.sup.−2, (FIG. 3 panel c) 2 mA h cm.sup.−2, (FIG. 3 panel d) 3 mA h cm.sup.−2, (FIG. 3 panel e) 4 mA h cm.sup.−2, (FIG. 3 panel f) 6 mA h cm.sup.−12 of Li into the three-dimensional porous hollow carbon fibers according to embodiment 1 of the present invention.

(4) FIG. 4 is a SEM image of the three-dimensional porous hollow carbon fiber current collector with a lithium load amount of 4 mA h cm.sup.−2 according to embodiment 1 of the present invention.

(5) FIG. 5 is a SEM image of the three-dimensional porous hollow carbon fiber current collector with a lithium load amount of 6 mA h cm.sup.−2 after 20 cycles according to embodiment 1 of the present invention.

(6) FIG. 6 is a charge-discharge curve of the three-dimensional porous hollow carbon fiber current collector with a lithium load amount of 4 mA h cm.sup.−2 at the current density of 1 mA cm .sup.−2 according to embodiment 1 of the present invention.

(7) FIG. 7 is a SEM image of the planar copper with a lithium load amount of 4 mA h cm.sup.−2 according to comparative sample 1 of the present invention.

(8) FIG. 8 is a SEM image of the planar copper with a lithium load amount of 4 mA h cm-2 after 10 cycles according to comparative sample 1 of the present invention.

(9) FIG. 9 shows the Coulombic efficiency of lithium plating/stripping on/from the three-dimensional porous hollow carbon fibers according to embodiment 1 and planar copper according to comparative sample 1.

EMBODIMENT

(10) The following further describes the present invention in combination with specific embodiments, and the present invention is not limited to the following implementation cases.

(11) The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial sources unless otherwise specified.

Embodiment 1

(12) (1) Preparation of Three-Dimensional Porous Hollow Carbon Fibers

(13) The biomass raw material cotton was repeatedly washed with ethanol and deionized water 3 times, dried, rolled, sliced, and calcined in the N.sub.2 atmosphere in a tube furnace at 1200° C., with the heating rate of 2° C./min for 3 hours. The raw materials are carbonized into hollow carbon fibers. After carbonization, stop heating, maintain the inlet of the protective gas, cool the reaction furnace to room temperature, and take out the sample. Then, the obtained sample was soaked with 1M activating reagent KOH for 5 hours, dried, and calcined in a protective atmosphere of nitrogen at 800° C. and 5° C./min heating rate for 2 hours. After activation, the activated sample was taken out, washed with diluted hydrochloric acid, washed repeatedly with deionized water and ethanol several times, and dried to obtain the desired three-dimensional hollow carbon fibers.

(14) From the SEM image of FIG. 1, the three-dimensional porous hollow carbon fibers structure can be clearly seen. It consists of intertwined carbon fibers with the diameter of about 10 μm, and the areal pore volume of 0.02 cm.sup.3 cm.sup.−2 (Mercury intrusion porosimetry).

(15) From the SEM image of FIG. 2, it can be clearly seen that the carbon fiber has hollow structure with the wall thickness of about 1 μm.

(16) (2) Preparation of a Lithium Metal Anode Using a Three-Dimensional Porous Hollow Carbon Fiber as the Current Collector

(17) The above-prepared three-dimensional porous hollow carbon fiber was used as the cathode, and the lithium foil was the anode. Lithium was electrochemically deposited on the three-dimensional porous hollow carbon fiber at the areal capacity of 1 mA h cm.sup.−2, 2 mA h cm.sup.−2, 3 mA h cm.sup.−2, 4 mA h cm.sup.−2, and 6 mA h cm.sup.−2, respectively.

(18) From the cross-section SEM images of FIG. 3, it can be clearly seen that the wall thickness of the hollow carbon fiber gradually increases as the lithium deposition capacity increases, indicating that a part of lithium metal is deposited on the wall of the hollow carbon fiber current collector. The hollow tube provides space for lithium deposition, which helps inhibit the growth of lithium dendrites and improve the safety, the Coulombic efficiency, and the cycle life of the battery.

(19) From the SEM image of FIG. 4, it can be clearly seen that another part of the metallic lithium is deposited along the framework of the three-dimensional hollow carbon fibers and filled in the pores between the carbon fibers without vertical growth of lithium dendrites.

(20) (3) Assembling Lithium Metal Secondary Batteries with the Above Anode

(21) The lithium metal secondary battery was prepared by assembling the metal anode with the three-dimensional porous hollow carbon fibers as the current collector, any suitable cathode and electrolyte.

(22) In the present embodiment, in order to test the safety and cycle life of the anode, half cells were assembled with lithium foil as the counter electrode and the above electrolyte to test the electrochemical performance of the three-dimensional porous hollow carbon fiber current collector.

(23) (4) Electrochemical Measurement of Lithium Metal Secondary Battery

(24) The charge-discharge apparatus was used for constant current charge-discharge test with the cut-off capacity of 4 mA h cm.sup.−2 and the test temperature of 25° C. FIG. 5 is a SEM image of the lithium anode after 20 cycles of the cycle test. It can be seen that the lithium surface is very smooth without lithium dendrites. FIG. 6 is the charge-discharge curve of the lithium anode at the current density of 1 mA h cm.sup.−2. The Coulombic efficiency of lithium plating/stripping reached 92% for the first time and about 99% after 10 cycles. After 100 cycles, the voltage remained stable and the polarization was small. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, no lithium dendrites were formed after 10 cycles.

Embodiment 2

(25) The only difference from Embodiment 1 is (1) preparation process of three-dimensional porous hollow carbon fibers. The carbonization temperature used is 800° C. The three-dimensional porous hollow carbon fiber current collector consists of intertwined carbon fibers with the areal pore volume of 0.01 cm.sup.3 cm.sup.−2 and the diameter of about 25 μm. The carbon fiber has hollow structure with the wall thickness of 5 μm.

(26) At the areal capacity of 4 mA h cm.sup.−2, the Coulombic efficiency of lithium plating/stripping was 80% for the first time and 97% after 10 cycles. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, no lithium dendrites were formed after 10 cycles.

Embodiment 3

(27) The only difference from Embodiment 1 is (1) preparation process of three-dimensional porous hollow carbon fibers. The carbonization temperature used is 1000° C. The three-dimensional porous hollow carbon fiber current collector consists of intertwined carbon fibers with the areal pore volume of 0.015 cm.sup.3 cm.sup.−2 and the diameter of about 15 μm. The carbon fiber has hollow structure with the wall thickness of 2 μm.

(28) At the areal capacity of 4 mA h cm.sup.−2, the Coulombic efficiency of lithium plating/stripping was 87% for the first time and 98% after 10 cycles. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, no lithium dendrites were formed after 10 cycles.

Embodiment 4

(29) The only difference from Embodiment 1 is (1) preparation process of three-dimensional porous hollow carbon fibers. The carbonization temperature used is 1400° C. The three-dimensional porous hollow carbon fiber current collector consists of intertwined carbon fibers with the areal pore volume of 0.025 cm.sup.3 cm.sup.−2 and the diameter of about 5 μm. The carbon fiber has hollow structure with the wall thickness of 0.8 μm.

(30) At the areal capacity of 4 mA h cm.sup.−2, the Coulombic efficiency of lithium plating/stripping was 90% for the first time and 96% after 10 cycles. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, no lithium dendrites were formed after 10 cycles.

Embodiment 5

(31) The only difference from Embodiment 1 is (1) preparation process of three-dimensional porous hollow carbon fibers. The processed cotton was first calcined at 700° C. for 1 h and then at 1200° C. for 2 h. The three-dimensional porous hollow carbon fiber current collector consists of intertwined carbon fibers with the areal pore volume of 0.018 cm.sup.3 cm.sup.−2 and the diameter of about 12 μm. The carbon fiber has hollow structure with the wall thickness of 1.2 μm.

(32) At the areal capacity of 4 mA h cm.sup.−2, the Coulombic efficiency of lithium plating/stripping was 90% for the first time and 98% after 10 cycles. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, no lithium dendrites were formed after 10 cycles.

Embodiment 6

(33) The only difference from Embodiment 1 is (1) preparation process of three-dimensional porous hollow carbon fibers. The obtained sample after carbonization was treated by 5M activating reagent KOH. The three-dimensional porous hollow carbon fiber current collector consists of intertwined carbon fibers with the areal pore volume of 0.016 cm.sup.3 cm.sup.−2 and the diameter of about 10 μm. The carbon fiber has hollow structure with the wall thickness of 1 μm.

(34) At the areal capacity of 4 mA h cm.sup.−2, the Coulombic efficiency of lithium plating/stripping was 90% for the first time and 98% after 10 cycles. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, no lithium dendrites were formed after 10 cycles.

Embodiment 7

(35) The only difference from Embodiment 1 is (1) preparation process of three-dimensional porous hollow carbon fibers. The calcination temperature of activation process was 600° C. The three-dimensional porous hollow carbon fiber current collector consists of intertwined carbon fibers with the areal pore volume of 0.012 cm.sup.3 cm.sup.−2 and the diameter of about 8 μm. The carbon fiber has hollow structure with the wall thickness of 0.75 μm.

(36) At the areal capacity of 4 mA h cm.sup.−2, the Coulombic efficiency of lithium plating/stripping was 85% for the first time and 97.5% after 10 cycles. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, no lithium dendrites were formed after 10 cycles.

Embodiment 8

(37) The only difference from Embodiment 1 is that the raw material used is cotton cloth. The three-dimensional porous hollow carbon fiber current collector consists of intertwined carbon fibers with the areal pore volume of 0.008 cm.sup.3 cm.sup.−2 and the diameter of about 20 μm. The carbon fiber has hollow structure with the wall thickness of 3.5 μm.

(38) At the areal capacity of 4 mA h cm.sup.−2, the Coulombic efficiency of lithium plating/stripping was 79% for the first time and 90% after 10 cycles. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, no lithium dendrites were formed after 10 cycles.

Embodiment 9

(39) The only difference from Embodiment 1 is that the raw material used is medical absorbent cotton. The three-dimensional porous hollow carbon fiber current collector consists of intertwined carbon fibers with the areal pore volume of 0.01 cm.sup.3 cm.sup.−2 and the diameter of about 30 μm. The carbon fiber has hollow structure with the wall thickness of 6 μm.

(40) At the areal capacity of 4 mA h cm.sup.−2, the Coulombic efficiency of lithium plating/stripping was 80% for the first time and 92% after 10 cycles. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, no lithium dendrites were formed after 10 cycles.

Embodiment 10

(41) The only difference from Embodiment 1 is that the raw material used is Degreasing cloth. The three-dimensional porous hollow carbon fiber current collector consists of intertwined carbon fibers with the areal pore volume of 0.005 cm.sup.3 cm.sup.−2 and the diameter of about 20 μm. The carbon fiber has hollow structure with the wall thickness of 4 μm.

(42) At the areal capacity of 4 mA h cm.sup.−2, the Coulombic efficiency of lithium plating/stripping was 78% for the first time and 89% after 10 cycles. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, no lithium dendrites were formed after 10 cycles.

Embodiment 11

(43) The only difference from Embodiment 1 is that the raw material used is polyacrylonitrile, using the method of coaxial electrospinning and then calcining. The three-dimensional porous hollow carbon fiber current collector consists of intertwined carbon fibers with the areal pore volume of 0.002 cm.sup.3 cm.sup.−2 and the diameter of about 35 μm. The carbon fiber has hollow structure with the wall thickness of 5.5 μm.

(44) At the areal capacity of 4 mA h cm.sup.−2, the Coulombic efficiency of lithium plating/stripping was 76% for the first time and 88% after 10 cycles. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, plenty of lithium dendrites were formed after 10 cycles.

Embodiment 12

(45) The only difference from Embodiment 1 is that the raw material used is polyvinyl alcohol fiber, using the method of pretreatment with iodine followed by carbonization. The three-dimensional porous hollow carbon fiber current collector consists of intertwined carbon fibers with the areal pore volume of 0.001 cm.sup.3 cm.sup.−2 and the diameter of about 40 μm. The carbon fiber has hollow structure with the wall thickness of 10 μm.

(46) At the areal capacity of 4 mA h cm.sup.−2, the Coulombic efficiency of lithium plating/stripping was 75% for the first time and 87% after 10 cycles. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, plenty of lithium dendrites were formed after 10 cycles.

Embodiment 13

(47) The only difference from Embodiment 1 is that the raw material used is lignin, using the method of coaxial electrospinning and then calcining. The three-dimensional porous hollow carbon fiber current collector consists of intertwined carbon fibers with the areal pore volume of 0.004 cm.sup.3 cm.sup.−2 and the diameter of about 20 μm. The carbon fiber has hollow structure with the wall thickness of 4 μm.

(48) At the areal capacity of 4 mA h cm.sup.−2, the Coulombic efficiency of lithium plating/stripping was 78% for the first time and 88% after 10 cycles. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, plenty of lithium dendrites were formed after 10 cycles.

Embodiment 14

(49) The only difference from Embodiment 1 is that the raw material used is polystyrene, using anodized aluminum as a template. The three-dimensional porous hollow carbon fiber current collector consists of intertwined carbon fibers with the areal pore volume of 0.001 cm.sup.3 cm.sup.−2 and the diameter of 300-400 nm. The carbon fiber has hollow structure with the wall thickness of 30 nm.

(50) At the areal capacity of 4 mA h cm.sup.−2, the Coulombic efficiency of lithium plating/stripping was 73% for the first time and 86% after 10 cycles. When the three-dimensional porous hollow carbon fiber current collector was loaded with 18 mA h cm.sup.−2 lithium metal, plenty of lithium dendrites were formed after 10 cycles.

(51) Comparative Sample 1

(52) Other conditions are the same as those of Embodiment 1, except that the planar copper foil is used as the current collector. The SEM image in FIG. 7 shows that filamentous lithium dendrites covered the surface of copper foil with the lithium load areal capacity of 4 mA h cm.sup.−2 lithium. After 10 cycles, it can be seen from the SEM image in FIG. 8 that part of the lithium dendrites grew in the vertical direction, which might eventually lead to an internal short circuit. In addition, plenty of inactive “dead lithium” was formed after only 10 cycles, which might lead to the decay of the Coulombic efficiency and shortening of the cycle life. FIG. 9 proves this very well. After a dozen cycles, Coulomb efficiency of the anode in comparative sample 1 was greatly attenuated, followed by large fluctuations. The voltage of lithium plating/stripping became unstable. The occurrence of side reaction caused the Coulombic efficiency to abnormally exceed 100%.

(53) Comparative Sample 2

(54) Other conditions are the same as those of Embodiment 1, except that the first embodiment of the prior art CN201110234427.4 is adopted as the current collector. Part of the lithium dendrites grew in the vertical direction with the lithium load areal capacity of 4 mA h cm.sup.−2 after 10 cycles, which might eventually lead to an internal short circuit. In addition, plenty of inactive “dead lithium” was formed, which might lead to the decay of the Coulombic efficiency and shortening of the cycle life.

(55) Comparative Sample 3

(56) Other conditions are the same as those of Embodiment 1, except that commercially available solid carbon fiber is adopted as the current collector. Part of the lithium dendrites grew in the vertical direction with the lithium load areal capacity of 4 mA h cm.sup.−2 after 10 cycles, which might eventually lead to an internal short circuit. In addition, plenty of inactive “dead lithium” was formed, which might lead to the decay of the Coulombic efficiency and shortening of the cycle life.

(57) In summary, when the three-dimensional porous hollow carbon fiber current collector of the present invention is used in the metal anode, the formation of lithium dendrites can be effectively suppressed, thereby improving the safety, Coulombic efficiency and cycle life of the metal anode.