CN111224076A - Electrode for inhibiting polysulfide ion shuttle in lithium-sulfur battery, preparation and application - Google Patents

Abstract

The invention relates to an electrode for inhibiting polysulfide ion shuttle flying in a lithium-sulfur battery, and preparation and application thereof. The sulfur-carbon electrode and the metal lithium cathode are assembled into the lithium-sulfur battery, so that the battery performance and the energy density can be greatly improved, and the lithium-sulfur battery has great potential for realizing future industrial large-scale production.

Description

Electrode for inhibiting polysulfide ion shuttle in lithium-sulfur battery, preparation and application

Technical Field

The invention relates to the technical field of lithium-sulfur batteries, in particular to a lithium-sulfur battery electrode and a preparation method thereof.

Background

The development of lithium-sulfur batteries has been gradually regarded as important since the 90 s of the last century because modern electronic devices require higher energy output, and lithium-sulfur batteries just can meet the requirement that they have very high theoretical energy density, the specific capacity of elemental sulfur reaches 1,675mAh/g, the specific mass energy reaches 2,600Wh/kg, and sulfur widely exists in nature, and data show that the abundance of sulfur in nature is about 0.048 wt%, and belongs to natural resources which are not fully utilized. Sulfur in nature exists mainly in the form of elemental sulfur (S8) which is thermodynamically stable at normal temperature. In addition, the elemental sulfur has the characteristics of low toxicity, low price, low density and the like. Despite its numerous advantages, there are still many problems to be solved, including the problem of shuttle of polysulfide ions as an intermediate product in charging and discharging of the positive electrode, the highly enriched lithium polysulfide causes an increase in the viscosity of the electrolyte, resulting in a decrease in the conductivity of the electrolyte, and seriously affecting the coulombic efficiency of the battery, resulting in a continuous decay of the cycle performance,

aiming at the shuttle effect caused by the dissolution and migration of the lithium polysulfide, researchers not only start from an electrolyte complexing agent and a diaphragm to inhibit the lithium polysulfide from shuttling to a negative electrode, but also mostly start from a positive electrode material, and inhibit the diffusion of the polysulfide from the positive electrode in a physical screening and chemical adsorption mode, wherein one idea is that a carbon material with multi-level pore channel distribution is adopted, on one hand, the carbon material is used for loading active substance sulfur with poor conductivity, on the other hand, the physical diffusion speed of the polysulfide is reduced through the small pore diameter of micropores, and on the other hand, the polarity of the carbon material can be changed by doping other atoms such as N, B and the like into the carbon material, and the polar polysulfide is adsorbed through a polar chemical bond. Although this strategy has achieved good results, its higher proportion of micropores results in a relatively low sulfur loading in the positive electrode, affecting the final cell energy density, and another idea is to apply a coating to the surface of the higher sulfur positive electrode, through which physical sieving or chemisorption effects are achieved to inhibit the polysulfide shuttling effect. Deposition of nano-sized TiO by ALD methods, for example₂Particles, vapor deposition of graphene coatings, and the like, in chemisorption and physical sieving processesThe surface obtains good effect of inhibiting polysulfide shuttle flying. However, it is difficult to satisfy the requirements of physical sieving, chemical adsorption, synergistic inhibition of polysulfide shuttle, improvement of electrode conductivity, and industrialization including low cost, mature and simple process.

Chemical plating is a coating technology with a mature process and is widely applied to the fields of aerospace, petrochemical industry and the like, and the coating deposited by the method has the characteristics of uniform thickness, high deposition speed and the like. The types of depositable elements are optional and include most of the eighth main group elements Fe, Co, Ni, Pd, and the like. Simultaneously, a plurality of metal oxides and ceramic materials such as TiO can be doped into the ceramic material₂、ZrO₂、SiO₂SiC, and the like. Due to the flexibility and the process maturity of the deposition method, the requirements can be well met, and the requirement for preparing the conductive coating capable of efficiently inhibiting polysulfide shuttles is very significant for realizing the industrialization of the high-energy-density lithium-sulfur battery.

The invention content is as follows:

in order to solve the technical problems, the invention prepares an electrode for inhibiting polysulfide ion shuttle flying in a lithium-sulfur battery, and the specific technical scheme is as follows:

depositing a Ni-based oxide composite layer on the surface of the electrode substrate containing sulfur, wherein the components of the Ni-based oxide composite layer comprise metallic nickel and metallic oxide, and the metallic oxide comprises TiO₂、SiO₂、ZrO₂One or more than two of them, the mass ratio of the metallic nickel and the metallic oxide is 2000:1-50: 1.

2. The electrode of claim 1, wherein: the thickness of the Ni-based oxide composite layer is 0.1-5 μm.

The electrode matrix comprises a carbon-sulfur compound, a binder and a conductive agent, wherein the carbon-sulfur compound is a mixture of active substances of sulfur and a carbon material, the sulfur accounts for 60-80 wt% of the total mass of the compound, the carbon-sulfur compound accounts for 60-90 wt% of the electrode matrix, the conductive agent accounts for 0-20 wt%, the binder accounts for 10-20 wt%, and the Ni-based oxide composite layer on the surface of the electrode matrix accounts for 1-15 wt% of the electrode matrix.

The carbon material comprises one or more than two of carbon nano tubes, graphene, carbon nano fibers, KB600, KB300 and Super-P; the conductive agent is one or more than two of carbon nano tube, graphene, carbon nano fiber, KB600, KB300 and Super-P;

the binder is one or two of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and Styrene Butadiene Rubber (SBR).

Depositing a Ni-based oxide composite layer on the surface of the electrode substrate by adopting a chemical plating method;

the specific operation process is as follows:

1) pretreatment of foamed nickel: placing the flaky foamed nickel with the thickness of 1mm-3mm in an aqueous solution of sulfuric acid, hydrochloric acid or nitric acid with the pH value of 2.0-5.0, carrying out activation pretreatment for 5-20 minutes, washing the treated foamed nickel with deionized water, and then closely contacting the foamed nickel with an electrode substrate;

2) the contact surface of the electrode substrate and the foamed nickel is subjected to chemical plating Ni-based oxide composite coating deposition modification: immersing the contacted flaky foamed nickel obtained in the step 1) and an electrode substrate into a plating solution; putting metal oxide particles into the plating solution; the mass concentration of the metal oxide in the transition liquid is 0.05-3 g/L; 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 mass concentration of the nickel salt in the plating solution is 10-50 g/L; the reducing agent is one or more than two of sodium hypophosphite, hydrazine hydrate and sodium borohydride, and the mass concentration of the reducing agent in the plating solution is 10-50 g/L; the complexing agent is one or more than two of EDTA, EGTA, sodium tartrate and sodium citrate, and has a mass concentration of 10-50g/L in the plating solution; the buffer is one or more than two of sodium acetate, ammonium acetate and ammonium chloride, and the mass concentration of the buffer in the plating solution is 10-50 g/L;

the plating solution is also added with a surfactant, the surfactant is one or more than two of sodium dodecyl benzene sulfonate, alkyl dimethyl betaine and octyl phenol polyoxyethylene ether, and the mass concentration of the surfactant in the plating solution is 0.005-0.2 g/L;

stabilizer is not added or added in the plating solution, the stabilizer is one or more than two of sodium thiosulfate, potassium iodide and thiourea, and the mass concentration in the plating solution is 0-0.1g/L, preferably 0.01-0.1 g/L; adjusting the pH value of the plating solution to 4.0-6.0 by adopting a pH regulator, and carrying out chemical plating, wherein the temperature is controlled to be 60-90 ℃ and the time is controlled to be 2 minutes-8 hours in the chemical plating process;

3) removing the foamed nickel in contact with the electrode to obtain the electrode with the Ni-based oxide composite layer deposited on the surface of the electrode substrate.

The pH regulator is hydrochloric acid or sulfuric acid solution with concentration of 100-400g/L, and sodium hydroxide or potassium hydroxide solution with concentration of 40-160 g/L.

The nickel salt in the chemical plating solution is preferably nickel phosphate, and the reducing agent is preferably sodium hypophosphite.

The metal oxide particles are of a size of 25-700 nm and the oxide particles comprise TiO₂、SiO₂、ZrO₂One or more than two of them.

The electrode matrix is formed by blade coating or electrostatic spinning of electrode matrix materials.

The electrode is applied to a secondary lithium-sulfur battery as a positive electrode, and the secondary lithium-sulfur battery comprises a positive electrode, a membrane and a negative electrode.

The beneficial results of the invention are:

the invention deposits a composite metal-oxide composite coating with high conductivity, physical screening and chemical adsorption polysulfide on the surface layer and the interior of the sulfur-carbon electrode material by adopting a chemical plating technology, and realizes the control of indexes such as components, thickness, appearance, uniformity and the like of the material coated on the surface and the interior of the electrode material by regulating and controlling the chemical plating deposition time, the chemical plating solution components, the particle size of the doped metal oxide and the pH value. The electrode has high conductivity, the utilization rate of active substances is improved, the shuttle flying of polysulfide is inhibited, and the cycle performance and the coulombic efficiency of the sulfur-carbon electrode are further improved.

Drawings

FIG. 1: chemical plating of Ni-P-TiO₂Front and rear electrode comparison.

FIG. 2: S/C electrode (b) and deposition of Ni-P-TiO₂(a) STEM comparison of the coatings.

FIG. 3: (ii) a Cyclic voltammetry tests of comparative example 1, comparative example 2 and example 1 electrodes.

FIG. 4: (ii) a Rate performance discharge curves at 0.1C-2C rate for the assembled button cells of comparative example 1, comparative example 2 and example 1.

FIG. 5: comparative example 1, comparative example 2 and example 1 pairs of cycling stability tests of assembled button cells.

FIG. 6: discharge curves of comparative example 3(a) and example 1(b) at different rates.

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 (S/C Positive electrode of Ni-P-PTFE without electroless deposition)

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 1g of PVDF-HFP binder in 36g N-methylpyrrolidone (NMP), stirring for 1h, adding 0.6g of conductive agents KB600 and 4g S/A-KB600, stirring for 4h, adjusting a scraper to 500 mu M, blade-coating the conductive agents on a glass plate to form a film, quickly immersing the film in water, taking out the film after 10min, placing the film in a freeze dryer for drying for 24h, taking out the film, shearing the film into small round pieces with the diameter of 10mm, weighing the small round pieces with the diameter of S/A-KB600, taking a lithium piece as a negative electrode and a celgard 2325 as a diaphragm, and adding 5 percent LiNO into 1M lithium bis (trifluoromethyl sulfonyl) imide (LiTFSI)₃The electrolyte solution is a mixed solution of 1, 3-Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) (volume ratio v/v is 1:1), the battery is assembled, the battery cycle performance test is carried out at 0.1C multiplying power, and the multiplying power is carried out at 0.1C-2C multiplying powerAnd (5) testing the performance.

The specific discharge capacity of the first circle under the multiplying power of 0.1C is 1034mAh g^-1The specific capacity is maintained to be 743mAh g after 100 cycles^-1(ii) a When the multiplying power is increased to 2C, the specific discharge capacity is 54mAh g^-1。

Comparative example 2 (S/C positive electrode of electroless deposition Ni-P coating)

The previous electrode slurry and electrode preparation process are the same as the comparative example 1, the electrode slurry and the electrode preparation process are carried out in a freeze dryer for 24 hours, then the electrode slurry and the electrode are closely contacted with foamed nickel with the thickness of 2mm, the foamed nickel is placed in hydrochloric acid aqueous solution with the pH value of 3 for 5 minutes, and then the electrode and the foamed nickel are placed in chemical plating solution with the temperature of 85 ℃ for 10 minutes to carry out chemical in-situ deposition of the metal nickel-phosphorus chemical coating. The chemical plating solution comprises 20g/L of nickel sulfate; 24g/L sodium hypophosphite; 15g/L sodium citrate; 0.01g/L thiourea; 15g/L sodium acetate; the solution PH was 4.8 and the thickness of the surface deposit coating obtained by electroless plating modification was about 1.5 μm. And drying the electrode deposited with the nickel-phosphorus 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 1. 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-2C. The specific discharge capacity of the first circle under the multiplying power of 0.1C is 1330mAh g^-1The specific capacity is maintained to 806mAh g after 100 cycles^-1(ii) a When the multiplying power is increased to 2C, the specific discharge capacity is 796mAh g^-1。

Comparative example 3 (atomic layer deposition of TiO on S/C cathode₂)

The preparation of the precursor electrode slurry and the electrode was the same as in comparative example 1, and then the atomic layer deposition technique was used to deposit about 1.5 μm TiO on the electrode₂The coating, with tetraisopropyl titanate and water as reactants, was subsequently assembled in a cell as in comparative example 1. The specific discharge capacity of the first circle under 0.1C multiplying power is 1150mAh g^-1When the multiplying power is increased to 2C, the specific discharge capacity is 175mAh g^-1。

Example 1 (electroless deposited Ni-P-TiO)₂S/C positive electrode of coating

The operation processes of preparing the electrode substrate and modifying the chemical plating are the same as the operation process of the comparative example 2, and the modulated parameter is in the chemical plating solutionAdding nano titanium dioxide particles with the particle size of about 50nm and the concentration of 1g/L TiO₂Particles, 0.01g/L of surfactant sodium dodecyl benzene sulfonate; the thickness of the deposited coating is about 1.5 mu m, and 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-2C.

The specific discharge capacity of the first circle under the multiplying power of 0.1C is 1530mAh g^-1The specific capacity after 100 cycles is maintained at 1023mAhg^-1(ii) a When the multiplying power is increased to 2C, the specific discharge capacity is 972mAh g^-1。

As shown in FIG. 1, a shows the original self-supporting sulfur-carbon anode material which is not deposited by electroless plating, b shows the original electrode surface which is deposited with Ni-P-TiO after electroless plating₂The coating can improve the current collecting effect of the electrode and the electron transmission efficiency in the electrode, realize higher utilization rate of active substances, inhibit the shuttle effect of polysulfide through physical screening and chemical adsorption and improve the cycle performance of the battery.

As shown in fig. 2, the surface of the electrode of example 1 after electroless deposition has a smaller pore size compared to the original electrode of example 1 without electroless deposition, so that the polysulfide can be effectively physically screened.

As shown in fig. 3, by testing the electrochemical properties of the cathode materials of comparative example 1, comparative example 2, and example 1 using cyclic voltammetry, example 1 exhibited a smaller electrochemical polarization than comparative example 1 and example exhibited a larger electrochemical capacity than comparative example 2 due to the deposition of a coating that is conductive and effective in inhibiting polysulfide shuttles. On one hand, the effective deposition of the Ni-P coating can greatly improve the electrical conductivity of the electrode, further improve the utilization rate of active substance sulfur and reduce polarization, and TiO is doped on the basis of the Ni-P coating₂The nano particles can ensure better conductivity of the electrode and further inhibit polysulfide from diffusing to the negative electrode, thereby improving the battery capacity.

As shown in fig. 4, batteries were assembled by using comparative example 1, comparative example 2 and example 1 as positive electrode materials and metallic lithium as negative electrode materials, and thenAnd (5) carrying out line multiplying power performance test. The reason why the example 1 shows higher specific discharge capacity than the comparative example 1 and the comparative example 2 under the 0.1C-2C rate is that the comparative example 2 and the example 1 have better conductivity of the electrode and better current collecting effect and can strengthen the conductive network in the electrode through the chemical plating deposition technology compared with the comparative example 1, thereby reducing the polarization of the electrode and improving the utilization rate of active substances. Example 1 addition of nano-titanium dioxide and TiO to Ni-P coating on the basis of comparative example 2₂The particles better retain the intermediate discharge product polysulfide at the positive electrode, and reduce the diffusion of the intermediate discharge product polysulfide to the negative electrode, so that the specific discharge capacity is further improved, and the embodiment 1 has the optimal performance in the rate performance test of the lithium-sulfur battery.

Fig. 5 shows that in the 0.1C battery cycle performance test, example 1 also showed better cycle performance than comparative example 1 and comparative example 2, with both the first cycle specific discharge capacity and the battery capacity after 100 cycles being greater than comparative example 1 and comparative example 2. The reason is also because of Ni-P-TiO deposited on the surface of the electrode₂The coating can well inhibit polysulfide from diffusing to the negative electrode while improving the current collecting effect and the electron transmission efficiency in the electrode, reduce the irreversible consumption with the lithium negative electrode and improve the utilization rate of active substances. Thus example 1 performed optimally in the lithium sulfur battery cycle performance test.

FIG. 6 shows pure TiO deposition₂Comparative example 3 of coating and Ni-P-TiO deposit₂Example 1 of the chemical coating discharge curves at different discharge rates, since even though TiO₂Polysulfide can be effectively chemisorbed, but the electrode polarization is larger due to the poorer conductivity, and particularly under high multiplying power, the discharge specific capacity is larger than the difference of example 1. Further illustrates example 1 by depositing Ni, TiO₂The method can improve the conductivity of the electrode and inhibit the synergistic effect of polysulfide shuttle so as to well improve the electrochemical performance of the sulfur-carbon electrode, thereby realizing the preparation of the high-specific-energy lithium-sulfur battery.

Claims (10)

1. An electrode for inhibiting polysulfide ion shuttle in a lithium sulfur battery, comprising:

depositing a Ni-based oxide composite layer on the surface of the electrode substrate containing sulfur, wherein the components of the Ni-based oxide composite layer comprise metallic nickel and metallic oxide, and the metallic oxide comprises TiO₂、SiO₂、ZrO₂One or more than two of them, the mass ratio of the metallic nickel and the metallic oxide is 2000:1-50: 1.

2. The electrode of claim 1, wherein: the thickness of the Ni-based oxide composite layer is 0.1-5 μm.

3. An electrode according to claim 1 or 2, wherein: the electrode matrix comprises a carbon-sulfur compound, a binder and a conductive agent, wherein the carbon-sulfur compound is a mixture of active substances of sulfur and a carbon material, the sulfur accounts for 60-80 wt% of the total mass of the compound, the carbon-sulfur compound accounts for 60-90 wt% of the electrode matrix, the conductive agent accounts for 0-20 wt%, the binder accounts for 10-20 wt%, and the Ni-based oxide composite layer on the surface of the electrode matrix accounts for 1-15 wt% of the electrode matrix.

4. The electrode of claim 3, wherein: the carbon material comprises one or more than two of carbon nano tubes, graphene, carbon nano fibers, KB600, KB300 and Super-P; the conductive agent is one or more than two of carbon nano tube, graphene, carbon nano fiber, KB600, KB300 and Super-P;

the binder is one or two of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and Styrene Butadiene Rubber (SBR).

5. A method of manufacturing an electrode according to any one of claims 1 to 4, wherein:

depositing a Ni-based oxide composite layer on the surface of the electrode substrate by adopting a chemical plating method;

the specific operation process is as follows:

1) pretreatment of foamed nickel: placing the flaky foamed nickel with the thickness of 1mm-3mm in an aqueous solution of sulfuric acid, hydrochloric acid or nitric acid with the pH value of 2.0-5.0, carrying out activation pretreatment for 5-20 minutes, washing the treated foamed nickel with deionized water, and then closely contacting the foamed nickel with an electrode substrate;

2) the contact surface of the electrode substrate and the foamed nickel is subjected to chemical plating Ni-based oxide composite coating deposition modification:

immersing the contacted flaky foamed nickel obtained in the step 1) and an electrode substrate into a plating solution; putting metal oxide particles into the plating solution; the mass concentration of the metal oxide in the transition liquid is 0.05-3 g/L;

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 mass concentration of the nickel salt in the plating solution is 10-50 g/L; the reducing agent is one or more than two of sodium hypophosphite, hydrazine hydrate and sodium borohydride, and the mass concentration of the reducing agent in the plating solution is 10-50 g/L; the complexing agent is one or more than two of EDTA, EGTA, sodium tartrate and sodium citrate, and has a mass concentration of 10-50g/L in the plating solution; the buffer is one or more than two of sodium acetate, ammonium acetate and ammonium chloride, and the mass concentration of the buffer in the plating solution is 10-50 g/L;

the plating solution is also added with a surfactant, the surfactant is one or more than two of sodium dodecyl benzene sulfonate, alkyl dimethyl betaine and octyl phenol polyoxyethylene ether, and the mass concentration of the surfactant in the plating solution is 0.005-0.2 g/L;

stabilizer is not added or added in the plating solution, the stabilizer is one or more than two of sodium thiosulfate, potassium iodide and thiourea, and the mass concentration in the plating solution is 0-0.1g/L, preferably 0.01-0.1 g/L;

adjusting the pH value of the plating solution to 4.0-6.0 by adopting a pH regulator, and carrying out chemical plating, wherein the temperature is controlled to be 60-90 ℃ and the time is controlled to be 2 minutes-8 hours in the chemical plating process;

3) removing the foamed nickel in contact with the electrode to obtain the electrode with the Ni-based oxide composite layer deposited on the surface of the electrode substrate.

6. The method for preparing an electrode according to claim 5, wherein:

the pH regulator is hydrochloric acid or sulfuric acid solution with concentration of 100-400g/L, and sodium hydroxide or potassium hydroxide solution with concentration of 40-160 g/L.

7. The method for preparing an electrode according to claim 5, wherein:

the nickel salt in the chemical plating solution is preferably nickel phosphate, and the reducing agent is preferably sodium hypophosphite.

8. The method for preparing an electrode according to claim 5, wherein:

the metal oxide particles are of a size of 25-700 nm and the oxide particles comprise TiO₂、SiO₂、ZrO₂One or more than two of them.

9. The method for preparing an electrode according to claim 5, wherein:

the electrode matrix is formed by blade coating or electrostatic spinning of electrode matrix materials.

10. Use of an electrode according to any of claims 1 to 4 as a positive electrode in a secondary lithium sulphur battery comprising a positive electrode, a membrane, a negative electrode.

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