Porous structure Si Cu composite electrode of lithium ion battery and preparation method thereof

Abstract

The present disclosure discloses a porous structure Si/Cu composite electrode of a lithium ion battery and a preparation method thereof. The composite electrode comprises an active substance, a bulk porous Cu and a current collector, wherein the active substance Si is embedded into the bulk porous Cu, and the bulk porous Cu is in metallurgical bonding with the current collector and plays a dual role of binder and conductive agent, which not only relieves the pulverization and the shedding of the active substance Si particles but also improves electron transmission efficiency; and meanwhile, the porous structure increases the contact area between the active substance Si and electrolyte and increases the reaction efficiency of lithium insertion combination. The method of preparing the composite electrode comprises: with Si, Cu and Al powders as raw materials, preparing a SiCuAl precursor alloy on the Cu current collector by powder metallurgy and diffusion welding technology; and removing Al element in the SiCuAl precursor alloy by using a chemical de-alloying method to obtain a Si/Cu composite electrode with a porous-structure.

Claims

1. A method for preparing a porous electrode, comprising: mixing powders of Si, Cu and Al to form a Si/Cu/Al material; performing a compression-moulding step on the Si/Cu/Al material; performing a sintering and diffusion welding step by pressing the compression-moulded Si/Cu/Al material and a Cu current collector together and putting the compression-moulded Si/Cu/Al material and the Cu current collector into a vacuum furnace to form a SiCuAl precursor alloy and to achieve a metallurgical bonding of the SiCuAl precursor alloy with the Cu current collector; and removing Al element in the SiCuAl precursor alloy by using a chemical etching method to obtain a porous Si/Cu composite electrode in metallurgical bonding with the Cu current collector.

2. The method of claim 1, wherein the weight percentages of the powders of Si, Cu and Al are 8-25% Si, 50-72% Cu, and the rest is Al.

3. The method of claim 1, wherein the sintering and diffusion welding step is performed with a temperature of 450-550 C. under a pressure of 0.2-1.0 MPa for 0.5-1.5 hours.

4. The method of claim 1, wherein an etchant used in the chemical etching method is selected from the group consisting of sodium hydroxide, potassium hydroxide, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and hydrofluoric acid.

5. The method of claim 4, wherein the concentration of the etchant used in the chemical etching method is 1-5 mol/L, and the etching time is 4-10 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a porous structure Si/Cu composite electrode of a lithium ion battery according to the present disclosure.

(2) FIG. 2 is a SEM view and an EDS element distribution view of a cross-section of a precursor alloy in the embodiment of FIG. 1.

(3) FIG. 3 is an XRD view of the precursor alloy in the embodiment of FIG. 1 after sintering and diffusion welding.

(4) FIG. 4 is a SEM view of a cross-section of the precursor alloy in the embodiment of FIG. 1 after de-alloying.

PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

(5) The present disclosure will be further described below in detail with reference to specific embodiments, but the present disclosure is not limited to the following embodiments.

(6) Herein, the term porous structure refers to an electrode structure that is formed by stacking small particles and has a porous-like structure, so as to facilitate the reaction and transfer of substances.

(7) Herein, the term active substance refers to a material with lithium intercalation capability.

(8) Herein, the term binder refers to a substance that is added for boding with active substances and can be removed or cannot be removed before or during sintering.

(9) Herein, the term conductive agent refers to an amount of conductive substance usually added when manufacturing the electrode piece in order to ensure that the electrode has a good charge-discharge performance, it plays a role of collecting micro-current between active substances and collecting micro-current between active substances and the current collector to decrease the contact resistance of the electrode so as to increase movement rate of electrons, and at the same time, can also effectively increase the migration rate of ions in electrode material, thereby increasing charge-discharge efficiency of the electrode.

(10) Here, the term current collector refers to a structure or component that collects electric current and its function is mainly to collect and export the electric current generated by the battery active substance.

(11) Here, the term powder refers to fine particles composed of dry and dispersed solid particles.

(12) As shown in FIG. 1, a porous electrode of a lithium ion battery comprising a bulk porous metal having a continuous porous structure; an active substance embedded into the porous structure of the bulk porous metal; and a current collector in metallurgical bonding with the bulk porous metal.

(13) In one embodiment, the material of the bulk porous metal is Cu. In one embodiment, the bulk porous metal has a pore size range of 10 to 20 m.

(14) In one embodiment, the material of the current collector can be Cu, stainless steel or Ni.

(15) In one embodiment, the active substance is Si particles. In one embodiment, the active substance has a particle size range of 100 nm to 45 m.

(16) The active substance Si is embedded into the block porous Cu, and the block porous Cu is in metallurgical bonding with the current collector to play a dual role of binder and conductive agent.

(17) For the characteristics of the composite electrode structure, the present disclosure also provides a corresponding manufacturing method comprising the following specific steps.

(18) Step 1: intensively mixing a certain proportion of three powders of Si, Cu and Al for compression moulding.

(19) Step 2: pressing the compression-moulded Si/Cu/Al material and a Cu current collector together and putting them into a vacuum furnace for sintering and diffusion welding to form a SiCuAl precursor alloy and to achieve a metallurgical bonding of the precursor alloy with the current collector.

(20) Step 3: removing Al element in the SiCuAl precursor alloy by using a chemical etching method to eventually obtain a porous Si/Cu composite electrode in metallurgical bonding with the current collector.

(21) In one embodiment, the weight percentages of material for preparing the precursor of the composite electrode are 8-25% Si, 50-72% Cu, and the rest is Al. When the content of Si is too low, the battery capacity is not high. When the content of Si is too high, the content of Cu or Al is necessarily decreased. When the content of Cu is too low, it is difficult to form a continuous porous Cu structure, and the active substance Si is prone to be pulverized and shed during the cycle of the battery. When the content of Al is too low, the porosity is low, and the electrolyte cannot sufficiently come into contact with the active substance Si, which decreases the reaction efficiency of lithium intercalation and lithium deintercalation. When the content of Cu is too high, the loading capacity of the active substance is deceased regardless of whether the content of Si or Al is reduced, which brings an adverse effect, and so is the case when the content of Al is too high.

(22) In one embodiment, the vacuum sintering and diffusion welding is performed with a temperature of 450-550 C. under a pressure of 0.2-1.0 MPa for 0.5-1.5 hours.

(23) In one embodiment, the etchant used in the chemical etching method is selected from the group consisting of sodium hydroxide, potassium hydroxide, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and hydrofluoric acid.

(24) In one embodiment, the concentration of the etchant used in the chemical etching method is 1-5 mol/L, and the etching time is 4-10 hours.

EXAMPLE 1

(25) Raw materials: Si, Cu, Al powders with a weight percentage of Si:Cu:Al=10:72:18, the mesh size of Si powder is 325 mesh, the mesh size of Cu powder is 300 mesh and mesh size of Al powder is 325 mesh.

(26) Etching solution: 3 M HCl solution.

(27) Preparation Process:

(28) Step 1, Compression Moulding

(29) Using Shanghai Xinnuo SYP-30T type compressing machine to perform compression moulding of the mixed Si/Cu/Al powder with a pressure of 0.4 MPa for 5 minutes to obtain a compression moulded Si/Cu/Al material with a diameter of 8 mm and a thickness of about 200 m. A SEM view and an EDS element distribution view of a cross-section of a precursor alloy of the material is shown in FIG. 2.

(30) Step 2, Sintering and Diffusion Welding

(31) By using the vacuum diffusion welding furnace HT-QA-25 produced by Beijing Hangtian Jinxiang Equipment Co., Ltd., the compression moulded Si/Cu/Al material is closely laminated to a Cu current collector, and then placed in the vacuum furnace and heated to 470 C. with an applied pressure of 0.4 MPa, and the temperature and pressure is maintained for 45 minutes. The atoms diffuse to form a strong metallurgical bonding. An XRD view of the precursor alloy after sintering and diffusion welding is shown in FIG. 3.

(32) Step 3, Chemical De-Alloying Processing

(33) The sample obtained by sintering and diffusion welding is immersed in HCl solution with a concentration of 3 mol/L for 4-10 hours, then washed with deionized water twice, and then put in HF ethanol solution with a mass percentage of 2% and stirred for 2 hours to dissolve SiO2 possibly presented on the surface of Si, and then washed with deionized water and absolute ethanol respectively for several times to obtain a porous structure Si/Cu composite electrode. A SEM view of a cross-section thereof is shown in FIG. 4.

EXAMPLE 2

(34) Raw materials: Si, Cu, Al powders with a weight percentage of Si:Cu:Al=14:72:14, the mesh size of Si powder is 325 mesh, the mesh size of Cu powder is 300 mesh and mesh size of Al powder is 325 mesh.

(35) Etching solution: 3 M HCl solution.

(36) Preparation Process:

(37) Step 1, Compression Moulding

(38) Using Shanghai Xinnuo SYP-30T type compressing machine to perform compression moulding of the mixed Si/Cu/Al powder with a pressure of 0.4 MPa for 5 minutes to obtain a compression moulded Si/Cu/Al material with a diameter of 8 mm and a thickness of about 200 m.

(39) Step 2, Sintering and Diffusion Welding

(40) By using the vacuum diffusion welding furnace HT-QA-25 produced by Beijing Hangtian Jinxiang Equipment Co., Ltd., the compression moulded Si/Cu/Al material is closely laminated to a Cu current collector, and then placed in the vacuum furnace and heated to 470 C. with an applied pressure of 0.4 MPa, and the temperature and pressure is maintained for 45 minutes. The atoms diffuse to form a strong metallurgical bonding.

(41) Step 3, Chemical De-Alloying Processing

(42) The sample obtained by sintering and diffusion welding is immersed in HCl solution with a concentration of 3 mol/L for 4-10 hours, then washed with deionized water twice, and then put in HF ethanol solution with a mass percentage of 2% and stirred for 2 hours to dissolve SiO2 possibly presented on the surface of Si, and then washed with deionized water and absolute ethanol respectively for several times to obtain a porous structure Si/Cu composite electrode.

EXAMPLE 3

(43) Raw materials: Si, Cu, Al powders with a weight percentage of Si:Cu:Al=25:50:25, the mesh size of Si powder is 325 mesh, the mesh size of Cu powder is 300 mesh and mesh size of Al powder is 325 mesh.

(44) Etching solution: 3M HCl solution.

(45) Preparation Process:

(46) Step 1, Compression Moulding

(47) Using Shanghai Xinnuo SYP-30T type compressing machine to perform compression moulding of the mixed Si/Cu/Al powder with a pressure of 0.4 MPa for 5 minutes to obtain a compression moulded Si/Cu/Al material with a diameter of 8 mm and a thickness of about 200 m.

(48) Step 2, Sintering and Diffusion Welding

(49) By using the vacuum diffusion welding furnace HT-QA-25 produced by Beijing Hangtian Jinxiang Equipment Co., Ltd., the compression moulded Si/Cu/Al material is closely laminated to the Cu current collector, and then placed in the vacuum furnace and heated to 470 C. with an applied pressure of 0.4 MPa, and the temperature and pressure is maintained for 45 minutes. The atoms diffuse to form a strong metallurgical bonding.

(50) Step 3, Chemical De-Alloying Processing

(51) The sample obtained by sintering and diffusion welding is immersed in HCl solution with a concentration of 3 mol/L for 4-10 hours, then washed with deionized water twice, and then put in HF ethanol solution with a mass percentage of 2% and stirred for 2 hours to dissolve SiO2 possibly presented on the surface of Si, and then washed with deionized water and absolute ethanol respectively for several times to obtain a porous structure Si/Cu composite electrode.

(52) Electrochemical Performance Test

(53) The performance of the porous structure Si/Cu composite electrode prepared in Example 1 is tested. The Wuhan LAND CT2001D test system is used during the test. The current density is taken as 100 mA/g, and the test result shows an areal capacity up to 9.6 mAh/cm2, the coulombic efficiency of the first discharge is 76% and the coulombic efficiency is maintained above 93% from the second charge-discharge. It can be seen that the composite electrode of the present disclosure has a good overall performance.

(54) The above-mentioned embodiments merely represent several embodiments of the present disclosure, and the description thereof is more specific and detailed, but it should not be understood as limiting the scope of the present disclosure. It should be noted that, for those skilled in the art, several variations and improvements may be made without departing from the concept of the present disclosure, and these are all within the protection scope of the present disclosure.