CN109873112B

CN109873112B - Electrode for secondary battery and preparation and application thereof

Info

Publication number: CN109873112B
Application number: CN201711246822.8A
Authority: CN
Inventors: 勾剑; 李先锋; 张华民; 张洪章; 杨晓飞; 陈雨晴; 于滢
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2017-12-01
Filing date: 2017-12-01
Publication date: 2021-06-22
Anticipated expiration: 2037-12-01
Also published as: CN109873112A

Abstract

The invention discloses an electrode for a secondary battery and preparation and application thereof, wherein the electrode realizes the in-situ deposition of a contact chemical plating process on an electrode matrix by using foamed nickel as a catalyst, so that the deposition of metallic nickel-phosphorus and a composite coating thereof is realized on the surface and inside of the electrode, thereby obviously improving the current collecting effect of the electrode, enhancing the electron transmission efficiency inside the electrode, realizing higher utilization rate of active substances, and ensuring that the thickness of the deposited coating on the surface of the electrode is 0.5-5 mu m; the electrode is applied to a secondary battery, can obviously improve the performance and the energy density of the battery, has simple operation process, mild experimental conditions and lower experimental cost, and has huge potential for realizing future industrialized large-scale production.

Description

Electrode for secondary battery and preparation and application thereof

Technical Field

The present invention relates to the field of secondary batteries, and in particular to a flexible high-capacity electrode.

Background

In recent years, with the increasing global energy and environmental crisis, lithium ion batteries and super capacitors have become the first choice power sources for various electronic products, such as notebook computers, electric bicycles, and other electronic devices. With the development of flexible electronics, people increasingly demand flexible and wearable media devices, such as OLED flexible smart phones, implantable devices, and the like, and these high-performance portable electronic devices also need to have higher-energy power output in addition to requiring that the equipped battery has good mechanical flexibility and miniaturization, so the research and development and preparation of high-affordability flexible electrodes are very important.

For the preparation of high-load flexible electrodes, the problem mainly faced is the current collection problem of the electrodes. In the process of preparing the electrode material, the traditional electrode preparation method is to coat the prepared electrode slurry on a metal film, the thickness of the metal film is usually about 10-25 μm, the metal film not only occupies certain electrode weight as a current collector, but also can be used as an inactive substance in the electrode material so as to reduce the volume and mass energy density, and in flexible equipment, the electrode material faces the problem that the active substance is peeled off from the film in the bending process of a battery so as to influence the current collecting effect of the electrode and further influence the battery performance. The existing method for preparing the flexible electrode mainly comprises the steps of replacing a metal film with materials with lighter weight, good mechanical property and excellent conductivity, such as graphene, carbon nanofiber and carbon nanotube, by vacuum filtration, vapor deposition and other process methods, so that the flexibility and the current collection effect of the electrode are improved. These methods have problems of high cost and complicated process. For high-load electrodes, the thickness of the electrode is generally thick, thus causing another problem of flexibility of the electrode itself, and bending and folding of the electrode often causes breakage of the electrode material and shedding of the internal active material. One of the methods is to increase the proportion of the binder in the electrode slurry, which results in a discontinuous conductive network inside the electrode, and is not favorable for the capacity exertion of the active material. And the problem of discontinuous conductive network caused by the increase of the content of the binder cannot be solved essentially by adding the conductive agents such as graphene and carbon nanotubes into the electrode slurry.

The chemical plating is used as an autocatalytic reaction, and the coating deposited by the method has the characteristics of uniform thickness, high deposition speed and the like. Electroless plating technology has been used to coat the interior walls of pipes in the second war, after which a series of electroless coatings such as Ni-W, Ni-P, Ni-B and the like began to develop and apply rapidly. In recent decades, electroless coatings have been commonly used in the fields of aviation, petrochemical industry, medical devices, etc. in the form of alloy coatings, composite coatings, metal coatings, etc., and among them, 95% of industrial electroless coatings use Ni-P, Ni-B-based alloy coatings, and especially Ni-P-based alloy coatings and composite coatings have been widely used in recent 10 years. The current method of carrying out chemical plating deposition on the flexible electrode material by a chemical plating method can well solve the problems of current collection and conductivity of a high-load flexible electrode, however, the adopted method usually uses an electroplating activation or chemical activation sensitization method to carry out pretreatment on the electrode material, and then carries out chemical plating deposition modification on the electrode material. This pretreatment step not only makes the process relatively complex, but also increases the production costs, such as the use of palladates. Therefore, the development of a simpler chemical plating deposition process to improve the current collecting and conducting efficiency of the flexible high-load electrode material is significant.

The invention content is as follows:

the invention provides a method for preparing a flexible high-load electrode by adopting foamed nickel as a contact catalyst and realizing the chemical plating deposition of nickel, phosphorus and a composite coating thereof on an electrode material directly through the close contact with the electrode material, thereby improving the current collecting and conducting efficiency of the flexible high-load electrode and omitting the step of electroplating activation or chemical activation sensitization pretreatment on an electrode material substrate.

The electrode takes foamed nickel as a catalyst, the foamed nickel is contacted with the outer surface of a plate-shaped electrode matrix on which a conductive substance is to be deposited, the chemical in-situ deposition of the electrode matrix is realized by adopting a contact chemical plating process, so that nickel-phosphorus or nickel-phosphorus composite coatings are deposited on the surface and inside of the electrode matrix, and the thickness of a metal coating on the surface of the electrode is 0.5-5 mu m; the electrode matrix material comprises an active substance, a conductive carbon material, a binder or the active substance and the binder, wherein the mass content of the active substance is 45-65%, the mass content of the conductive carbon material is 0-30%, the mass content of the binder is 20-35%, and the mass content of the nickel-phosphorus or nickel-phosphorus composite coating deposited on the surface and in the electrode matrix accounts for 0.05-8wt% of the electrode.

The conductive carbon material comprises one or more than two of carbon nano tubes, graphene, carbon nano fibers, KB600, KB300 and Super-P.

The binder is one or more of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).

The active substance is one or more than two of sulfur, lithium iron phosphate and lithium titanate.

The preparation method of the electrode comprises the following steps of,

1) foam nickel pretreatment: putting the foamed nickel into an aqueous solution of sulfuric acid, hydrochloric acid or nitric acid with the pH value of 2.0-5.0 for 5-20 minutes, and then washing the foamed nickel by deionized water;

2) stacking the pretreated foamed nickel and the surface-to-surface layer of the plate-shaped electrode substrate according to claims 1 to 4, fixing the foamed nickel by using a clamp or a rubber band to ensure that the surface of the foamed nickel is in close contact with the surface of the plate-shaped electrode substrate, and placing the foamed nickel in chemical plating solution;

3) carrying out chemical plating of Ni-P and modification of a composite coating of the Ni-P to an electrode material: the chemical plating solution comprises an aqueous solution consisting of nickel salt, a reducing agent, a complexing agent and a buffering agent; the nickel salt is one or more of nickel chloride, nickel sulfate, nickel phosphate and nickel acetate, and the concentration is 10-50 g/L;

the reducing agent is sodium hypophosphite with the mass concentration of 10-50 g/L; the complexing agent is one or more than two of EDTA, EGTA, sodium tartrate and sodium citrate, and the final mass concentration is 10-50 g/L; the buffer is one or more than two of sodium acetate, ammonium acetate and ammonium chloride, and the final mass concentration is 10-50 g/L;

compound salt or solution is not added or can be added in the chemical plating solution, and the compound salt or solution comprises one or more than two of cobalt salt, tin salt, PTFE aqueous solution and PVDF aqueous solution; the cobalt salt is one or more than two of cobalt sulfate, cobalt chloride and cobalt acetate, the tin salt is tin chloride, the final concentrations of the cobalt salt and the tin salt in the plating solution are respectively 10-50g/L, 1-7ml of 10wt% PTFE aqueous solution can be put into each liter of plating solution, and 10wt% PVDF aqueous solution can be put into each liter of plating solution;

the pH value of the plating solution is between 4.0 and 5.0 or between 8.0 and 9.5; the temperature is controlled between 60 ℃ and 90 ℃ and the time is controlled between 15 minutes and 8 hours in the chemical plating process.

The chemical plating solution also comprises a stabilizer which is one or more than two of sodium thiosulfate, potassium iodide and thiourea, and the final mass concentration of the stabilizer is 0.01-0.1 g/L.

The pH regulator is adopted to regulate the pH of the plating solution, and the pH regulator is 100-400g/L hydrochloric acid or sulfuric acid solution; 40-160g/L sodium hydroxide or ammonia solution.

The electrode is applied to a secondary battery as a positive electrode and/or a negative electrode, and the secondary battery consists of the positive electrode, a membrane and the negative electrode.

The nickel salt in the electroless plating solution is preferably nickel phosphate.

The electrode matrix is formed by adopting electrode matrix material blade coating film formation or electrostatic spinning film formation.

The beneficial results of the invention are:

the invention realizes the deposition of metal nickel phosphorus and a composite coating thereof on the surface layer and inside of the electrode by adopting foamed nickel as a contact catalyst for the electrode material, and realizes the control of indexes such as components, thickness, morphology and the like of the material coated on the surface and inside of the electrode material by adjusting the chemical plating time, the chemical plating solution components and the pH value. Therefore, the polarity, surface energy, conductivity and the like of the chemical plating coating are regulated and controlled, the utilization rate of active substances is improved, the cycle life of the chemical plating coating is prolonged, the traditional current collector metal film is replaced, and the electrochemical performance and the battery performance of the battery are improved while the flexibility of the electrode is ensured. The chemical plating modification process is simple to operate, mild in experimental conditions and low in cost, and has great potential for realizing future industrial large-scale production.

Drawings

FIG. 1: photographs of the electrode of comparative example 1 (left panel) and the electrode of example 2 (right panel);

FIG. 2: example 2 interfacial SEM (left) and partial magnified SEM images (right);

FIG. 3: rate performance discharge curves at 0.1C-1C rate for lithium sulfur cells assembled as comparative example 1, comparative example 2, examples 1 and 2;

FIG. 4: cycle stability testing of lithium sulfur batteries assembled with comparative example 1, comparative example 2, examples 1 and 2;

FIG. 5: comparative example 2 and example 2.

Detailed Description

The following examples are further illustrative of the present invention and are not intended to limit the scope of the present invention. Comparative example 1 (self-supporting electrode without electroless deposition of nickel, phosphorus, cobalt)

20g of commercial KB600 was placed in a tube furnace under Ar protection at 5 ℃ for min^-1Heating to 900 deg.C, introducing steam for activation for 1.5h, wherein the flow rate of steam is 600mL min^-1The activated carbon material was designated A-KB 600. Mixing 10g A-KB600 and 20g S, heating to 155 deg.C in a tube furnace at a heating rate of 1 deg.C for min^-1Keeping the temperature constant for 20 hours, and recording the obtained product as S/A-KB600, wherein the sulfur filling amount is 75 percent. Dissolving 2g of PVDF-HFP binder in 40g N-methylpyrrolidone (NMP), stirring for 1h, adding 4g S/A-KB600, stirring for 4h, adjusting a scraper to 1500 mu m, coating the film on a glass plate, quickly immersing the film in water, taking out the film after 10min, drying the film at 65 ℃ overnight, shearing the film into small round pieces with the diameter of 10mm, weighing the small round pieces, drying the small round pieces in vacuum at 60 ℃ for 24h, and taking the small round pieces coated with the S/A-KB600 as a positive electrode (the sulfur carrying amount of each round piece is about 2.2mg cm)^-2) Lithium sheet as negative electrode, celgard 2325 as diaphragm, 1M lithium bis (trifluoromethylsulfonyl) imide solution (LiTFSI) plus 5% LiNO₃The electrolyte solution was a mixed solution of 1, 3-Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) (volume ratio v/v 1:1), the cell was assembled, and the cell cycle performance test was performed at 0.1C rate and the rate performance test was performed at 0.1C-1C rate.

The specific discharge capacity of the first circle under 0.1C multiplying power is 530mAh g^-1The specific capacity is maintained to be 143mAh g after 100 cycles^-1(ii) a When the multiplying power is increased to 1C, the specific discharge capacity is 50mAh g^-1. The sulfur content is about 12mg/cm^-2。

Comparative example 2 (without nickel-phosphorus-cobalt plating, electrode coated on Al foil)

The preparation of the electrode slurry is the same as the operation process of the comparative example 1, the electrode slurry is coated on an aluminum film in a blade mode to form a film, the film is quickly immersed into water, the film is taken out after 10min, dried at 65 ℃ overnight, cut into small round pieces with the diameter of 10mm, weighed and dried in vacuum at 60 ℃ for 24 h. Subsequent cell assembly was the same as comparative example. The assembled battery is subjected to a battery cycle performance test at a rate of 0.1C, and a rate performance test at a rate of 0.1C-1C.

The specific discharge capacity of the first ring is 840mAh g^-1Capacity after 100 cycles was maintained at 325mAh g^-1(ii) a When the multiplying power is increased to 1C, the specific discharge capacity is 280mAh g^-1。

Example 1

2g of binder PVDF-HFP are dissolved in 40g N-methyl pyrrolidone (NMP), stirred for 1h, added with 4g S/A-KB600 (sulfur charging 75%), stirred for 4h, adjusted to 1500 μm, blade-coated to form a film on a glass plate (without using a metal film as a current collector), then the glass plate together with the electrode coating blade-coated thereon is rapidly immersed in water, after 10min the electrode coating is peeled off and taken out of the glass plate, and dried at 65 ℃ overnight. The method comprises the steps of placing 60 mm-60 mm foamed nickel with the thickness of 1mm in one of sulfuric acid aqueous solutions with the pH value of 2.0-5.0 for 10 minutes to carry out activation pretreatment, cleaning the treated foamed nickel with deionized water, and binding the cleaned foamed nickel with an electrode material through a rubber band to enable the surface of the foamed nickel to be in close contact with the front side and the back side of a self-supporting flexible electrode. Then placing the obtained product in an electroless plating solution at 90 ℃ for 10 minutes to carry out chemical in-situ deposition of metallic nickel, phosphorus and cobalt. The chemical plating solution comprises 20g/L of nickel sulfate; 24g/L sodium hypophosphite; 20g/L cobalt sulfate; 15g/L sodium citrate; 0.01g/L thiourea; 15g/L sodium acetate; the solution PH was 9, and the thickness of the surface-deposited nickel layer obtained by electroless plating modification was about 0.5 μm. And drying the electrode with the deposited nickel layer at 65 ℃ overnight, cutting the electrode into small wafers with the diameter of 10mm, weighing the wafers, and performing vacuum drying at 60 ℃ for 24 hours. Subsequent cell assembly was the same as comparative example. The assembled battery is subjected to a battery cycle performance test at a rate of 0.1C, and a rate performance test at a rate of 0.1C-1C.

The specific discharge capacity of the first ring is 1130mAhg^-1Capacity after 100 cycles is maintained at 606mAhg^-1(ii) a When the multiplying power is increased to 1C, the specific discharge capacity is 670mAh g^-1。

Example 2

The operation process of preparing the electrode substrate and the operation process of chemical plating modification are the same as the operation process of the embodiment 1, the modulation parameters are that the chemical plating time is 30 minutes, the thickness of the nickel layer deposited on the surface of the electrode is about 1 mu m, the assembled battery is subjected to a battery cycle performance test at a multiplying power of 0.1C, and a multiplying power performance test at a multiplying power of 0.1C-1C.

The specific discharge capacity of the first ring is 1300mAh g^-1Capacity after 100 cycles is maintained at 800mAh g^-1(ii) a When the multiplying power is increased to 1C, the specific discharge capacity is 840mAh g^-1。

As shown in the left and right figures of FIG. 1, the surface of the lithium sulfur anode material modified by chemical plating deposition can be deposited with a nickel-phosphorus-cobalt coating with metallic luster, the coating can replace the traditional metal film current collector and has better conductivity, and as shown in FIG. 2, the coating has deposition on the two sides of the electrode, is denser, is uniformly deposited on the surface of the electrode, and has the thickness of about 1 μm.

As shown in fig. 3, the batteries using comparative example 2 and comparative example 1 as the positive electrode material have a higher specific discharge capacity at 0.1C-1C rate in the case of containing the positive electrode material, because the comparative example 2 uses a metallic Al foil as the current collector to achieve a better current collecting effect than the comparative example 1, and the examples 1 and 2 use an electroless plating process to achieve deposition of a metal coating on the front and back sides and the inside of the electrode, thereby enhancing the electron transport efficiency inside the electrode while replacing the conventional current collector, and suppressing the shuttle effect of polysulfide to exhibit better battery rate performance at 0.1C-1C rate than the comparative examples 1 and 2. Example 2 is the optimum electrode in the rate performance test of lithium-sulfur battery, and the thickness of the nickel layer deposited on the surface of the electrode is about 1.0 μm.

As shown in fig. 4, in the 0.1C battery cycle performance test, examples 1 and 2 also exhibited better cycle performance than comparative example 2 and comparative example 1, and both the specific discharge capacity at the first cycle and the battery capacity after 100 cycles were greater than those of comparative example 1 and comparative example 2. The reason is that the nickel-phosphorus-cobalt coating deposited on the surface of the electrode can improve the current collecting effect and the electron transmission efficiency in the electrode, and simultaneously can well inhibit the shuttle effect of polysulfide and improve the utilization rate of active substances. Example 2 is the optimum electrode in the cycle performance test of the lithium sulfur battery, and the thickness of the nickel layer deposited on the surface of the electrode is 1.0 μm.

Fig. 5 shows a comparison of the adhesion of the electrode material when the electroless deposited nickel phosphorous cobalt coating was compared to an aluminum foil as a current collector and quantified by measuring its peel force.

In the case that the peeling force of example 2 is slightly larger than that of comparative example 2, the nickel-phosphorus-cobalt coating deposited on the surface of the electrode of example 2 can still adhere well to the electrode after peeling, while the electrode using the conventional current collector aluminum foil as the current collector of comparative example 2, after peeling, the electrode active material is basically separated from the aluminum foil. The chemical plating process adopting the nickel foam as the contact catalyst can deposit the metal nickel phosphorus and the composite coating thereof which are bonded with the electrode matrix more tightly, and well replace the traditional metal foil film current collector. Synthesizing the high-load flexible electrode material with excellent performance.

Claims

1. An electrode for a secondary battery, characterized in that: the electrode uses foam nickel as a catalyst, the foam nickel is contacted with the outer surface of a plate-shaped electrode matrix on which a conductive substance is to be deposited, the chemical in-situ deposition of the electrode matrix is realized by adopting a contact chemical plating process, so that a nickel-phosphorus or nickel-phosphorus composite coating is deposited on the surface and inside of the electrode matrix, and the thickness of the nickel-phosphorus or nickel-phosphorus composite coating on the surface of the electrode is 0.5-5 mu m; the electrode matrix material is active substance, conductive carbon material, binder or active substance and binder, wherein the mass content of the active substance is 45-65%, the mass content of the conductive carbon material is 0-30%, the mass content of the binder is 20-35%, and the mass content of the nickel-phosphorus or nickel-phosphorus composite coating deposited on the surface and in the electrode matrix accounts for 0.05-8wt% of the electrode;

the electrode is prepared by the following steps:

step 1) foam nickel pretreatment: putting the foamed nickel into an aqueous solution of sulfuric acid, hydrochloric acid or nitric acid with the pH value of 2.0-5.0 for 5-20 minutes, and then washing the foamed nickel by deionized water;

step 2) stacking the pretreated foamed nickel and the surface of the plate-shaped electrode substrate opposite to each other, fixing the foamed nickel and the surface of the plate-shaped electrode substrate by using a clamp or a rubber band to ensure that the surface of the plate-shaped electrode substrate is in close contact with the surface of the plate-shaped electrode substrate, and placing the plate-shaped electrode substrate in chemical plating solution;

step 3) carrying out chemical nickel-phosphorus plating or nickel-phosphorus composite coating modification on the electrode material: the chemical plating solution comprises an aqueous solution consisting of nickel salt, a reducing agent, a complexing agent and a buffering agent; the nickel salt is one or more of nickel chloride, nickel sulfate, nickel phosphate and nickel acetate, and the concentration is 10-50 g/L;

the pH value of the plating solution is between 4.0 and 5.0 or between 8.0 and 9.5; the temperature is controlled between 60 and 90 during the chemical plating process^oAnd C, controlling the time between 15 minutes and 8 hours.

2. The electrode of claim 1, wherein: the conductive carbon material comprises one or more than two of carbon nano tubes, graphene, carbon nano fibers, KB600, KB300 and Super-P.

3. The electrode of claim 1, wherein: the binder is one or more of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).

4. The electrode of claim 1, wherein: the active substance is one or more than two of sulfur, lithium iron phosphate and lithium titanate.

5. A method of preparing an electrode according to any one of claims 1 to 4, wherein: the method comprises the following steps:

step 2) stacking the pretreated foamed nickel and the surface-to-surface layer of the plate-shaped electrode substrate according to claims 1 to 4, fixing the surface-to-surface layer by using a clamp or a rubber band to ensure that the surface-to-surface layer is in close contact with the surface-to-surface layer, and placing the surface-to-surface layer in chemical plating solution;

6. The method according to claim 5, wherein the electroless plating solution further comprises a stabilizer selected from the group consisting of sodium thiosulfate, potassium iodide and thiourea, and the stabilizer has a final mass concentration of 0.01 to 0.1 g/L.

7. The preparation method according to claim 5, characterized in that the pH of the plating solution is adjusted by using a pH adjusting agent which is a hydrochloric acid or sulfuric acid solution with a concentration of 100-400 g/L; 40-160g/L sodium hydroxide or ammonia solution.

8. Use of an electrode according to any of claims 1 to 4 as a positive and/or negative electrode in a secondary battery consisting of a positive electrode, a membrane and a negative electrode.