CN116154124A - Preparation of lithium-sulfur battery positive electrode material with surface gel function - Google Patents

Abstract

The invention discloses a preparation method of a lithium-sulfur battery positive electrode material with a surface gel function, and belongs to the technical field of energy storage and conversion materials. The preparation method comprises the steps of preparing a hydroxyl transition metal oxide precursor by adopting a chemical reduction method at room temperature, and then performing an autoxidation decomposition process to prepare the nano two-dimensional hydroxyl transition metal oxide. Stirring the lithium-sulfur battery positive electrode material and the nano two-dimensional transition metal oxyhydroxide to ensure that the nano two-dimensional oxyhydroxide is spontaneously and uniformly coated on the surface of positive electrode particles, thereby constructing the novel lithium-sulfur battery positive electrode composite material. The nano two-dimensional hydroxyl transition metal oxide synthesized by the method modulates the microscopic electronic structure of the material, improves the reactivity, promotes the ring-opening polymerization of the 1, 3-dioxolane in the ether-based electrolyte, realizes in-situ surface gelation, effectively inhibits the side reaction, volume expansion and intermediate product dissolution of the material in the charge-discharge process, and has high specific capacity, high volume energy density and excellent cycle stability.

Description

Preparation of lithium-sulfur battery positive electrode material with surface gel function

Technical Field

The invention discloses a preparation method of a lithium-sulfur battery positive electrode material with a surface gel function, belongs to the field of lithium-sulfur batteries, and is used for preparing gel lithium-sulfur batteries.

Background

Lithium sulfur batteries are of continued interest due to the ultra-high theoretical energy density (2600 Wh/kg) and low cost advantages. Taking a soft package lithium sulfur battery which is more nearly practical as an example, the storable energy per kilogram is twice as much as that of the traditional commercial lithium ion battery at present, and the performance superiority of the lithium sulfur battery is more obvious for applications such as unmanned aerial vehicles, soldier carrying power packages and the like which relate to the national defense field.

Unlike the deintercalation mechanism in conventional lithium ion batteries, the discharge process of lithium sulfur batteries involves polysulfide ions of different valence states (S _n ^2- N is more than or equal to 1 and less than or equal to 8), the problems of capacity attenuation, low utilization rate of active substances, slow conversion kinetics and the like caused by shuttling of lithium polysulfide are plagued by the application of the lithium sulfur battery, and the modification of the sulfur anode is a main way for improving the electrochemical performance of the lithium sulfur battery. Thus, limiting migration of the induced soluble lithium polysulfide by surface gelation is beneficial in slowing or eliminating the "shuttle effect" of lithium polysulfide.

Compared with gel initiators used in other lithium sulfur batteries, the hydroxyl transition metal oxide has the following special problems: (1) The hydroxyl transition metal oxide has low intrinsic electronic conductivity, so that the activity is poorer than that of other initiators, (2) the hydroxyl transition metal oxide prepared by the traditional mode has smaller specific surface area and insufficient exposure of active sites, so that the reactivity is lower. Therefore, the ideal hydroxyl transition metal oxide material in the lithium sulfur battery needs to have higher electron conductivity and more reactive sites, and based on an efficient active material limiting mechanism, the active material sulfur in the lithium sulfur battery is ensured to be limited to the positive electrode side, the advantage of high specific capacity of the sulfur positive electrode is exerted, and meanwhile, the stability and the service life of the charging and discharging process of the lithium sulfur battery are obviously improved.

The combination of the hydroxyl transition metal oxide and the carbon material can improve the reactivity of the material and inhibit the dissolution of the lithium sulfur polymer, such as the amorphous iron oxyhydroxide-biochar composite material disclosed in CN 112691666A. However, there are many problems to be solved in the current methods for preparing hydroxyl transition metal oxides, including the combination with carbon: (1) The hydroxyl transition metal oxide is mainly synthesized by wet reaction, and the material often contains a large amount of impurities. (2) Hydroxyl transition metal oxides are usually prepared into nano particles so as to increase active sites, but interface side reactions of nano particle materials are greatly increased, agglomeration is easy, and the nano particles are difficult to disperse in an aqueous solution system. (3) In the design of compounding with the carbon material, the carbon material is easily dissolved during the lithium-sulfur battery reaction process, resulting in a short circuit of the battery.

Disclosure of Invention

Aiming at the problem of circulation stability in application in lithium sulfur batteries, the invention provides a preparation method of a lithium sulfur battery positive electrode material with a surface gel function, which has the advantages of enriching oxygen vacancies and having negative surface Zeta potential, and the preparation method and application in the lithium sulfur batteries, and solves the technical problems that the hydroxyl iron oxide material has poor conductivity and small specific surface area and is difficult to combine with the lithium sulfur battery positive electrode. Therefore, in order to enhance the reactivity of the hydroxylmethyl metal oxide and allow the hydroxylmethyl metal oxide to be effectively combined with the sulfur cathode, a nano-hydroxylmethyl metal oxide having a structure rich in oxygen vacancies is constructed to achieve this object. Specifically, the design targets of the preparation method are as follows: controlling the microscopic morphology of the hydroxyl transition metal oxide, preparing a two-dimensional nano sheet, enabling the two-dimensional nano sheet to have a large specific surface area, and increasing a reactive site; the microcoordination structure of the hydroxy transition metal oxide is controlled to have a large number of oxygen vacancy defects, thereby increasing the conductivity of the material and making the Zeta potential of the surface of the material in a weakly acidic aqueous solution (pH between 5 and 7) take on negative values. Meanwhile, the Zeta potential of the lithium-sulfur battery positive electrode material in the weak acid aqueous solution is positive, nano hydroxyl transition metal oxide can be induced to be uniformly wrapped on the surface of the positive electrode material through electrostatic action, and under the electro-hydraulic infiltration condition, the polymerization reaction of the electrolyte on the surface of the sulfur positive electrode is initiated in situ, polysulfide is limited on the positive electrode side, the shuttle effect is inhibited, the utilization rate of active substances is improved, and the electrochemical reversibility in the long-term circulation process is ensured.

The invention solves the problems by adopting the technical scheme that: the preparation method of the lithium-sulfur battery positive electrode material with the surface gel function comprises the following steps:

dissolving 0.03-0.18 mol of transition metal salt in 100mL of distilled water, protecting under the condition of nitrogen, dripping distilled water solution dissolved with a reducing agent and an alkaline compound into the transition metal salt solution at the speed of 100-200 r/min at room temperature, and stirring for 1-2 h; after the reducing agent and the alkaline compound solution are added dropwise, continuing stirring and reacting for 1-3 hours to obtain a nano two-dimensional hydroxyl transition metal oxide precursor; dissolving a nano two-dimensional hydroxyl transition metal oxide precursor in an alcohol solvent, and stirring for 12-48 hours at a rotating speed of 500-800 rpm in an open environment at room temperature to obtain a nano two-dimensional hydroxyl transition metal oxide; placing nano two-dimensional hydroxyl transition metal oxide into 100mL of weak acid aqueous solution, stirring for 2-5 hours at the pH value of 5-7 and the rotating speed of 100-200 r/min, then placing 1-5 g of lithium sulfur battery positive electrode material, stirring for 1-2 hours at the rotating speed of 100-200 r/min, obtaining a product, respectively washing the product with 50-100 mL/r of methanol and 50-100 mL/r of deionized water for 2 times, and drying for 12 hours under the vacuum degree of-0.01-0.02 Mpa to obtain the nano two-dimensional hydroxyl transition metal oxide-coated lithium sulfur battery positive electrode composite material;

the transition metal salt is one or more of ferric nitrate, ferric chloride, ferric sulfate, ferrous sulfate, ferric oxalate, 2-hydroxy propionic acid iron, ferric carboxylate, nickel nitrate, nickel chloride, nickel sulfate, nickel oxalate, cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt oxalate, manganese nitrate, manganese chloride, manganese sulfate and manganese oxalate; the molar concentration of the transition metal salt in the transition metal salt solution is 0.3-1.8 mol/L;

the reducing agent is more than one of sodium sulfite, stannous chloride, oxalic acid, potassium borohydride, sodium borohydride and ethanol; the mol ratio of the transition metal salt to the reducing agent is 1:1.5-5.5;

the alkaline compound is more than one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate and sodium dihydrogen phosphate; the mass ratio of the total mass of the transition metal salt and the reducing agent to the alkaline compound is 1:0.05-0.1;

the alcohol solvent is more than one of methanol, ethanol, glycol and diethylene glycol;

the weak acid aqueous solution is one or more of acetic acid, carbonic acid, silicic acid, nitrous acid, hydrogen sulfuric acid, hydrofluoric acid, hypochlorous acid, hydrocyanic acid, sulfurous acid and phosphoric acid solution;

the mass ratio of the nano two-dimensional hydroxyl transition metal oxide to the lithium sulfur battery positive electrode material is 100:1.0 to 10.0;

the lithium sulfur battery anode material is one or more of elemental sulfur, a carbon sulfur composite material and an organic polysulfide compound, wherein the carbon sulfur composite material is a mesoporous carbon-based sulfur composite material, a carbon nanotube-based carbon sulfur composite material or a graphene-based carbon sulfur composite material, and the organic polysulfide compound is vulcanized polyacrylonitrile, cyanuric acid or vulcanized polypropylene.

The invention has the beneficial effects that: (1) The current preparation method of the hydroxyl transition metal oxide precursor is that oxygen-containing gas with the oxygen component ratio of 0.5-0.8 is blown into the suspension liquid in the temperature range of more than-5 ℃ but less than 10 ℃; the temperature for preparing the precursor is controlled at room temperature, no additional oxygen is needed to be blown in, and the full and slow dropwise addition of the reducing agent is beneficial to the full reaction and reduces impurities;

(2) The currently ubiquitous method for preparing a hydroxyl transition metal oxide comprises controlling the suspension of a hydroxyl transition metal oxide particle precursor within a temperature range of 20 ℃ or more but less than 45 ℃ and blowing an oxygen-containing gas into the suspension, thereby generating hydroxyl transition metal oxide particles from the hydroxyl transition metal oxide particle precursor; according to the preparation method, the hydroxyl transition metal oxide particle precursor is subjected to autoxidation treatment, the nano two-dimensional hydroxyl transition metal oxide precursor is dissolved in an alcohol solvent, and is subjected to vigorous stirring in an open environment at room temperature, so that the nano two-dimensional hydroxyl transition metal oxide is obtained, the oxygen supply is not needed, and the alcohol solvent with low dissolved oxygen is used, so that the oxidation process of the precursor is in an anoxic state, and the increase of oxygen vacancies is facilitated. The exact active site is found to be derived from oxygen vacancy to induce lattice distortion, so that conductivity is promoted, and reactivity is improved;

(3) By adjusting the coordination environment, the electronegative Zeta potential is constructed, and the electronegative Zeta potential is spontaneously combined with the high-sulfur-load lithium sulfur battery positive electrode material in a weak acid water system environment. The invention starts from the design of the hydroxyl transition metal oxide, effectively utilizes the advantages of a two-dimensional nano structure and a coordination environment, excites the reaction activity of the hydroxyl transition metal oxide, enables the ether electrolyte to polymerize on the surface of the positive electrode in situ, inhibits the shuttle effect caused by the dissolution of long-chain sulfur, improves the utilization rate of active substances, and provides a novel technical approach for obtaining higher specific capacity and higher energy density of the lithium-sulfur battery.

Drawings

FIG. 1 is a Transmission Electron Microscope (TEM) image of the synthesized nano two-dimensional iron oxyhydroxide

In the figure: (a) A scanning electron microscope (TEM) image after the combination of the nano two-dimensional ferric oxide hydroxide and the lithium sulfur battery, and a Scanning Electron Microscope (SEM) image after the combination of the nano two-dimensional ferric oxide hydroxide and the lithium sulfur battery.

FIG. 2 shows a Zeta potential diagram of synthesized nano two-dimensional ferric hydroxide and a Zeta potential diagram of a lithium sulfur battery positive electrode material

In the figure: -Zeta potential results for nano two-dimensional iron oxyhydroxide, -Zeta potential results for lithium sulfur positive electrode material;

the X-axis is Zeta potential in mV and the Y-axis is intensity in a.u..

FIG. 3 is a comparative graph of spectroscopic tests of nano two-dimensional nickel oxyhydroxide and nickel oxyhydroxide prepared by conventional methods

In the figure: (a) The electron paramagnetic resonance spectrum of the nano two-dimensional nickel oxyhydroxide and the electron paramagnetic resonance spectrum of the nickel oxyhydroxide prepared by the common method are compared, wherein the X axis is a magnetic field H, the unit is Gauss, the Y axis is electron paramagnetic, and the unit is a.u./mg;

(b) The test result of the pore and specific surface area of nano two-dimensional nickel oxyhydroxide shows that the X-axis is relative pressure and the unit is P/P _o The Y-axis represents the adsorption cc/g.

FIG. 4 is a graph showing electrochemical cycle performance of the synthesized nano two-dimensional manganese oxyhydroxide-coated lithium-sulfur cathode material

In the figure: ● A coulombic efficiency curve is given as a discharge specific capacity curve, and 1c=1000 mAh/g;

the abscissa is the number of cycles, the unit is n, the ordinate is the specific discharge capacity, and the unit is mAh/g; the right ordinate is coulombic efficiency in%.

Detailed Description

The invention is described in further detail below with reference to the drawings and examples.

Example 1

Dissolving 0.03mol of ferric nitrate in 100mL of distilled water, protecting under the condition of nitrogen, dropwise adding distilled water solution dissolved with a reducing agent and a trace amount of alkaline compound into the ferric nitrate solution at 0.1mL/min, and stirring for 1h at the room temperature and the rotating speed of 100 revolutions per min; after the sodium sulfite and sodium hydroxide solution are added dropwise, continuing stirring and reacting for 1h to obtain a nano two-dimensional ferric hydroxide precursor, wherein the molar ratio of ferric nitrate to sodium sulfite is 1:1.5, and the mass ratio of the total mass of ferric nitrate to sodium sulfite to sodium hydroxide is 1:0.05; dissolving a nano two-dimensional hydroxyl ferric oxide precursor in an ethanol solvent, and stirring for 12 hours at a rotating speed of 500 revolutions per minute in an open environment at room temperature to obtain a nano two-dimensional hydroxyl transition metal oxide; placing nano two-dimensional hydroxyl transition metal oxide into 100mL of weak acid aqueous solution, stirring for 2 hours at the pH value of 5 and the rotation speed of 100 r/min, then placing 1g of lithium sulfur battery positive electrode material, stirring for 1 hour at the rotation speed of 100 r/min, washing the obtained product with 50 mL/m methanol and 50 mL/m deionized water for 2 times respectively, and drying for 12 hours in vacuum (vacuum degree-0.01 Mpa) to obtain the nano two-dimensional hydroxyl ferric oxide coated lithium sulfur battery positive electrode composite material.

Fig. 1 is a Transmission Electron Microscope (TEM) image (see fig. 1 (a)) of the nano-two-dimensional iron oxyhydroxide synthesized in example 1, and a Scanning Electron Microscope (SEM) image (see fig. 1 (b)) of the nano-two-dimensional iron oxyhydroxide combined with a lithium sulfur battery. As can be seen from FIG. 1, the material has a stable structure and a nano-sheet structure characteristic, and the average thickness dimension is 5nm. Fig. 2 is a Zeta potential diagram of the nano two-dimensional iron oxyhydroxide synthesized in example 1 and a Zeta potential diagram of a positive electrode material of a lithium sulfur battery. From the test results, the Zeta potential of the nano two-dimensional ferric hydroxide is-24.3 mV, and the Zeta potential of the positive electrode of the lithium-sulfur battery is +8.7mV, so that the two materials can be combined through electrostatic action.

Example 2

Dissolving 0.09mol of nickel chloride in 100mL of distilled water, protecting under the condition of nitrogen, dropwise adding distilled water solution dissolved with a reducing agent and a trace amount of alkaline compound into the nickel chloride solution at the speed of 1mL/min, and stirring for 1.5h at the room temperature at the speed of 150 rpm; after the stannous chloride and potassium hydroxide compound solution are added dropwise, continuing stirring and reacting for 2 hours to obtain a nano two-dimensional nickel oxyhydroxide precursor, wherein the molar ratio of the nickel chloride to the stannous chloride is 1:3.0, and the mass ratio of the total mass of the nickel chloride to the stannous chloride to the potassium hydroxide is 1:0.10; dissolving a nano two-dimensional nickel oxyhydroxide precursor in a methanol solvent, and stirring for 24 hours at a rotating speed of 650 revolutions per minute in an open environment at room temperature to obtain nano two-dimensional nickel oxyhydroxide; placing nano two-dimensional nickel oxyhydroxide into 100mL of weak acid aqueous solution, stirring for 3 hours at the pH value of 6 and the rotation speed of 150 rpm, then placing 3g of lithium sulfur battery positive electrode material, stirring for 1.5 hours at the rotation speed of 150 rpm, washing the obtained product with 80 mL/time of methanol and 80 mL/time of deionized water for 2 times respectively, and drying in vacuum (vacuum degree-0.015 Mpa) for 12 hours to obtain the nano two-dimensional nickel oxyhydroxide-coated lithium sulfur battery positive electrode composite material.

FIG. 3 is a graph showing the results of pore and specific surface area measurements of nano-sized two-dimensional nickel oxyhydroxide synthesized in example 2 (see FIG. 3 (a)) and the electron paramagnetic resonance spectrum of nano-sized two-dimensional cobalt oxyhydroxide and nickel oxyhydroxide prepared by conventional methods (see FIG. 3 (b)). As can be seen from FIG. 1, the porosity of the nano two-dimensional nickel oxyhydroxide was 0.43cm ³ Per gram, specific surface area of 185.9m ² The large specific surface and high porosity of the composition facilitate the adequate exposure of the active sites,thereby rapidly realizing in-situ gelation; in the electron paramagnetic resonance spectrum, when g=2.003, larger fluctuation proves that the synthesized nano two-dimensional nickel oxyhydroxide has a large number of oxygen vacancies compared with the nickel oxyhydroxide prepared by the common method, and the nano two-dimensional nickel oxyhydroxide prepared by the method has stronger activity.

Example 3

Dissolving 0.18mol of cobalt chloride in 100mL of distilled water, protecting under the condition of nitrogen, dropwise adding 2mL/min of distilled water solution dissolved with a reducing agent and a trace amount of alkaline compound into the cobalt chloride solution, and stirring for 3 hours at room temperature at the rotating speed of 200 revolutions/min; after the solution of potassium borohydride and sodium bicarbonate is completely added dropwise, continuing stirring and reacting for 2 hours to obtain a nanometer two-dimensional cobalt oxyhydroxide precursor, wherein the molar ratio of cobalt chloride to stannous chloride is 1:5.5, and the mass ratio of the total mass of the cobalt chloride to the stannous chloride to potassium hydroxide is 1:0.75; dissolving a nano two-dimensional cobalt oxyhydroxide precursor in an ethylene glycol solvent, and stirring for 48 hours at a rotating speed of 800 revolutions per minute in an open environment at room temperature to obtain nano two-dimensional cobalt oxyhydroxide; placing nano two-dimensional cobalt oxyhydroxide into 100mL of weak acid aqueous solution, stirring for 5 hours at the pH value of 6.5 and the rotation speed of 150 rpm, then placing 5g of lithium sulfur battery positive electrode material, stirring for 1.5 hours at the rotation speed of 150 rpm, and washing the obtained product with 100 mL/time of methanol and 100 mL/time of deionized water for 2 times respectively, and drying for 12 hours in vacuum (vacuum degree-0.02 Mpa) to obtain the nano two-dimensional cobalt oxyhydroxide-coated lithium sulfur battery positive electrode composite material.

The prepared nano two-dimensional cobalt oxyhydroxide-coated lithium-sulfur battery positive electrode composite material is used as an electrode material of a lithium-sulfur battery, and the electrolyte is a traditional lithium-sulfur electrolyte. Fig. 4 is an electrochemical performance diagram of the lithium sulfur battery positive electrode composite material wrapped by nano two-dimensional cobalt oxyhydroxide synthesized in example 3 as an electrode material of a lithium sulfur battery. The initial specific discharge capacity is 1382.6mAh/g under the condition that the electrolyte and active material ratio is 3 under the current density of 1C (1 C=1000 mA/g) in the voltage range of 1.8-2.5V, the initial coulomb efficiency is 96.2%, and the reversible capacity is 693.2mAh/g after 250 cycles.

Claims (1)

1. The preparation method of the lithium-sulfur battery positive electrode material with the surface gel function is characterized by comprising the following steps of:

dissolving 0.03-0.18 mol of transition metal salt in 100mL of distilled water, protecting under the condition of nitrogen, dripping distilled water solution dissolved with a reducing agent and an alkaline compound into the transition metal salt solution at the speed of 100-200 r/min at room temperature, and stirring for 1-2 h; after the reducing agent and the alkaline compound solution are added dropwise, continuing stirring and reacting for 1-3 hours to obtain a nano two-dimensional hydroxyl transition metal oxide precursor; dissolving a nano two-dimensional hydroxyl transition metal oxide precursor in an alcohol solvent, and stirring for 12-48 hours at a rotating speed of 500-800 rpm in an open environment at room temperature to obtain a nano two-dimensional hydroxyl transition metal oxide; placing nano two-dimensional hydroxyl transition metal oxide into 100mL of weak acid aqueous solution, stirring for 2-5 hours at the pH value of 5-7 and the rotating speed of 100-200 r/min, then placing 1-5 g of lithium sulfur battery positive electrode material, stirring for 1-2 hours at the rotating speed of 100-200 r/min, obtaining a product, respectively washing the product with 50-100 mL/r of methanol and 50-100 mL/r of deionized water for 2 times, and drying for 12 hours under the vacuum degree of-0.01-0.02 Mpa to obtain the nano two-dimensional hydroxyl transition metal oxide-coated lithium sulfur battery positive electrode composite material;

the transition metal salt is one or more of ferric nitrate, ferric chloride, ferric sulfate, ferrous sulfate, ferric oxalate, 2-hydroxy propionic acid iron, ferric carboxylate, nickel nitrate, nickel chloride, nickel sulfate, nickel oxalate, cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt oxalate, manganese nitrate, manganese chloride, manganese sulfate and manganese oxalate; the molar concentration of the transition metal salt in the transition metal salt solution is 0.3-1.8 mol/L;

the reducing agent is more than one of sodium sulfite, stannous chloride, oxalic acid, potassium borohydride, sodium borohydride and ethanol; the mol ratio of the transition metal salt to the reducing agent is 1:1.5-5.5;

the alkaline compound is more than one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate and sodium dihydrogen phosphate; the mass ratio of the total mass of the transition metal salt and the reducing agent to the alkaline compound is 1:0.05-0.1;

the alcohol solvent is more than one of methanol, ethanol, glycol and diethylene glycol;

the weak acid aqueous solution is one or more of acetic acid, carbonic acid, silicic acid, nitrous acid, hydrogen sulfuric acid, hydrofluoric acid, hypochlorous acid, hydrocyanic acid, sulfurous acid and phosphoric acid solution;

the mass ratio of the nano two-dimensional hydroxyl transition metal oxide to the lithium sulfur battery positive electrode material is 100:1.0-10.0;

the lithium sulfur battery anode material is one or more of elemental sulfur, a carbon sulfur composite material and an organic polysulfide compound, wherein the carbon sulfur composite material is a mesoporous carbon-based sulfur composite material, a carbon nanotube-based carbon sulfur composite material or a graphene-based carbon sulfur composite material, and the organic polysulfide compound is vulcanized polyacrylonitrile, cyanuric acid or vulcanized polypropylene.

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