CN114649516B

CN114649516B - Lignin carbon/nickel oxide nano composite material and preparation method and application thereof

Info

Publication number: CN114649516B
Application number: CN202210187686.4A
Authority: CN
Inventors: 杨东杰; 陈其亮; 邱学青; 楼宏铭; 李致贤; 黄思; 黄锦浩; 易聪华; 刘伟峰; 欧阳新平
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2022-02-28
Filing date: 2022-02-28
Publication date: 2023-03-21
Anticipated expiration: 2042-02-28
Also published as: CN114649516A

Abstract

The invention discloses a lignin carbon/nickel oxide nano composite material and a preparation method and application thereof. The method comprises the steps of firstly purifying lignosulfonate by low-concentration sulfuric acid, then adjusting the concentration of a carbonate solution to provide an alkaline solution environment, then slowly adding a sulfanilate solution, a nickel salt solution and an aldehyde compound solution, carrying out high-pressure hydrothermal reaction, and finally carbonizing to obtain the lignin carbon/nickel oxide nano composite material. The lignin carbon and the nickel oxide in the material exist in a nanoscale manner, so that the problems of severe volume expansion and poor conductivity when the nickel oxide is used as a lithium ion battery cathode material are effectively solved, and the specific capacity, the cycling stability and the rate capability of the lithium ion battery are improved.

Description

Lignin carbon/nickel oxide nano composite material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a lignin carbon/nickel oxide nano composite material and a preparation method and application thereof.

Background

The lithium ion battery has the advantages of high energy density, long cycle life, no memory effect, low self-discharge rate and the like, and is widely applied to the fields of new energy automobiles, portable electronic equipment, aerospace equipment and the like. The cathode material is one of the main components of the lithium ion battery, and directly influences the electrochemical performance of the lithium ion battery.

The lithium ion battery cathode material mainly comprises a carbon material, a silicon-based material, a tin-based material, an alloy material, a transition metal, an oxide thereof and the like. The graphite carbon material has the advantages of low cost, rich raw material reserves, excellent conductivity, good lithium ion intercalation/deintercalation performance and the like, becomes a preferred choice of a commercial lithium ion battery cathode material, and occupies a leading position in the market. However, the graphite negative electrode material has the disadvantages of low theoretical capacity (372 mAh/g), low ion diffusion coefficient caused by too narrow spacing between carbon layers, potential safety hazard caused by easy formation of lithium dendrite during high-rate charge and discharge, and the like, and is difficult to meet the current requirements of people on high-performance lithium ion batteries. Therefore, there is an urgent need to develop a safe and efficient new lithium ion battery negative electrode material to replace commercial graphite.

In recent years, transition metal oxides have received much attention as negative electrode materials for lithium ion batteries. The nickel oxide has the theoretical capacity of 718mAh/g, is rich in reserve, low in price, easy to obtain and good in corrosion resistance, and has a good application prospect when being used as a lithium ion battery cathode material. However, nickel oxide has the following two main problems, which severely restrict the application and development of nickel oxide in the negative electrode material of the lithium ion battery: (1) In the charging and discharging process, the volume expansion rate of nickel oxide exceeds 90%, agglomeration, cracking and pulverization are easy to occur, so that the electrode material loses electrochemical activity, the battery capacity is reduced, and the cycling stability is poor; (2) The electronic conductivity of nickel oxide is low, and the rate capability is poor.

In order to solve these two problems of nickel oxide, researchers have proposed various methods to improve the lithium storage performance of nickel oxide, and the main ideas can be divided into the following two types:

(1) Starting from the microstructure of nickel oxide, the size of the nickel oxide is reduced, and the nano nickel oxide with good dispersibility is designed. The nano-scale nickel oxide can effectively relieve the volume expansion effect, improve the circulation stability, effectively shorten the diffusion path of lithium ions and electrons, and improve the rate capability of the nickel oxide. The good dispersibility can reduce the voltage polarization of the nickel oxide and improve the cycle performance. Varghese et al (chem. Mater. (2008) 20 (10): 3361) prepared nickel oxide nanowalls using chemical vapor deposition with RF plasma generator assisted oxidation, the material remained at a specific capacity of about 700mAh/g after 40 cycles at a current density of 448mA/g while storing lithium. However, the high specific surface area provided by nanocrystallization aggravates the agglomeration problem of the material, so that the specific capacity of the material is still reduced after a certain number of charge-discharge cycle processes, and meanwhile, the preparation process is complex and difficult for large-scale production. Chinese patent application CN103151182A discloses a nano nickel oxide electrode material, which takes lignosulfonate as a template, nickel ions and alkaline substances are introduced in a solution state to generate precipitates, the lignosulfonate template is removed after filtration and air calcination, and the nano nickel oxide is obtained. Liu and the like (Journal of Materials Chemistry (2011) 21. Hu et al (Energy & Environmental Science (2016) 9. The conclusion also has guiding significance for the structural design of the nano nickel oxide. Relevant research reports of Sun et al (Advanced Energy Materials (2014) 4 (4): 1300912), elizabeth et al (electrochemical Acta (2017) 230) 98-105) and Feng et al (Journal of Power Sources (2016) 301. It should be noted, however, that the process for preparing pure phase nano nickel oxide with particle size less than 10nm is often too complicated to be implemented.

(2) The compounding of the nano nickel oxide and the carbon material with good conductivity and structural strength is a main strategy for improving the lithium storage performance of the nickel oxide, and the compounding of the nickel oxide and the carbon not only relieves the volume expansion effect of the nano nickel oxide but also can improve the electronic conductivity of the material, thereby obviously improving the electrochemical performance. Tian and the like (Electrochimica Acta (2018) 261, 236-245) firstly use yeast as a template to prepare hollow nickel oxide microspheres, then a layer of glucose is coated on the surface of the hollow nickel oxide microspheres through hydrothermal treatment, and carbonization is carried out to obtain the carbon-coated nickel oxide hollow composite material, the material has the specific discharge capacity of 628mAh/g after being circulated for 100 times under the current density of 100mA/g, the cycle performance is good, and the good performance of the material is mainly due to the carbon-coated hollow sphere structure, so that the expansion of nickel oxide is effectively inhibited. Feng et al (J.Mater.chem.A, (2016) 4, 3267-3277) hydrothermally prepare nickel hydroxide, then coat glucose on the surface of the nickel hydroxide, and obtain a nickel oxide/carbon composite material after carbonization reduction and air oxidation calcination, wherein the nickel oxide/carbon composite material is used as a lithium ion battery cathode material and has a discharge specific capacity of 1168mAh/g after circulating for 200 times at a current density of 500 mA/g. Zou et al (Nanoscale (2011) 3) and Han et al (Journal of Alloys and Compounds (2020) 848). Generally, the process difficulty of compounding the nano nickel oxide and the carbon material is relatively low, and the method is an effective method for improving the electrochemical performance of the nickel oxide. However, most of carbon sources commonly used for being compounded with nickel oxide are graphene, graphene oxide, organic high molecular compounds such as glucose and other chemicals, or plant straws, plant roots and other biomass. The former has the problems of high price, partial toxicity and difficulty in large-scale production, and the latter is limited by a natural structure, lacks of structure designability, and the size of the composite material is often larger, so that the uniform dispersion of the nano nickel oxide is not facilitated.

The lignin is a macromolecule with an amorphous three-dimensional network structure formed by linking three phenylpropane structural units through carbon-carbon bonds and ether bonds, has the advantages of high carbon content, high thermal stability, good mechanical strength, structural design and the like, and is an ideal precursor for preparing a carbon-based material in the nickel oxide/carbon composite material. At present, the composite material taking lignin carbon as a carbon source has made a certain progress in the aspect of being used as a lithium ion battery negative electrode material, and relevant documents and analysis thereof are as follows:

li Changqing and the like (advanced school chemistry bulletin (2018) 39 (12): 2725-2733) use nano-silica as a template, prepare a lignin carbon/silica composite material through hydrothermal treatment, carbonization and acid washing, have a discharge specific capacity of 820mA/g after 100 times of circulation under a current density of 100mA/g, have good circulation performance, and can buffer the volume expansion of the silica to a certain extent, but the lignin carbon directly uses commercial silica with a particle size of 20nm, so that the amount of the silica in the composite is less than 10% in order to prevent the silica from expanding. The Chinese patent application CN112072085A uses enzymatic hydrolysis lignin and zinc acetate to carry out hydrothermal compounding, the generated nano zinc oxide is used as a template, and a lignin nano carbon/zinc oxide composite material is prepared through carbonization and acid washing, the specific discharge capacity of the material is 705mAh/g after the material is circulated for 200 times under the current density of 200mA/g during lithium storage, the cycle performance is excellent, but the specific discharge capacity under 1000mA/g is only 360mAh/g, which is mainly because the lignin nano carbon coated outside the composite material is thick, the lithium storage of the internal zinc oxide is limited, the ion transmission is blocked under the high current density, and the multiplying power performance is poor. Xi, and the like (Industrial Crops & Products (2021) 161.

When the composite material taking the lignin carbon as the carbon skeleton is used as the lithium ion battery negative electrode material, the volume expansion effect of active components such as silicon dioxide, tin oxide or zinc oxide and the like can be relieved to a certain extent, and the electrochemical performance is improved, however, the dispersibility of the lignin carbon and the active components is not obviously improved or the sizes of the lignin carbon and the active components are not reduced in the reports of the documents, so that the lithium storage performance of the related composite material still has a space for further improving.

In the aspect of using the lignin carbon and nickel oxide composite material as the lithium ion battery negative electrode material, the reports of related documents are few, and the main reports are as follows: chen et al (Green Chemistry (2013) 15, 3057-3063) add sodium lignosulfonate into an ethanol solution of nickel nitrate, then add cross-linking agents formaldehyde and glutaraldehyde, polymerize at a low temperature of 80 ℃, and finally carbonize in an argon atmosphere at 600 ℃ to obtain a lignin carbon/nickel oxide composite material, wherein the lignin carbon/nickel oxide composite material has a high specific capacitance of 880.2F/g at a current density of 1000mA/g as a supercapacitor electrode. However, because the lignin carbon in the composite material is formed by crosslinked macromolecular sodium lignosulfonate, the dispersion is poor, the agglomeration is serious, and the composite material lacks good structural toughness and mainly has a disordered stacking structure, most of nickel oxide is limited in the lignin carbon or completely coated in a disordered carbon layer, and the phenomena of large particle size and serious agglomeration exist, so that the material cannot effectively solve the problems of the volume expansion effect and poor conductivity of the nickel oxide, and is not beneficial to improving the lithium storage capacity. Chinese patent application CN112928233A discloses a preparation method of a nickel oxide-lignin carbon composite material with a core-shell structure and application thereof in a lithium ion battery cathode. The method comprises the steps of taking alkali lignin as a carbon source, firstly preparing polyethyleneimine grafted lignin microspheres, then adsorbing inorganic nickel by using the lignin microspheres to obtain nickel-based lignin microspheres, then putting the nickel-based lignin microspheres into a tubular furnace for carbonization to obtain a core-shell structure nitrogen-doped carbon coated nickel oxide compound, and finally mixing the compound with potassium hydroxide for secondary carbonization to obtain a core-shell structure nickel oxide-lignin carbon composite material, wherein the charge specific capacity is 854.2mAh/g after the composite material is cycled for 200 times at a current density of 100mA/g during lithium storage. According to the method, the porous core-shell composite structure is prepared, and the coating effect of the porous carbon spheres is utilized, so that the problem of volume expansion of nickel oxide is relieved to a certain extent, the rapid capacity attenuation of the nickel oxide cathode material is avoided, and the capacity retention rate and the cycling stability are improved. However, the preparation method of the material is too complex, the process is long, and the process comprises two carbonization processes, so that the energy consumption is high, and the material is not beneficial to industrial application. Zhou et al (Electrochimica Acta (2018) 274. When the material is used as a lithium ion battery cathode, the discharge specific capacity can still be kept at about 500mAh/g under the heavy current density of 1000mA/g, the rate capability is excellent, but the cycle performance is poor. The reason is that the size of the lignin carbon spheres in the composite material is still larger than 100nm, the structural strength of the lignin carbon spheres is poor, and a certain agglomeration phenomenon exists, so that the cycle stability of the composite material is reduced to a certain extent.

In summary, the problems of low lithium storage capacity and poor cycle stability generally exist when the lignin carbon/nickel oxide composite material prepared by the prior art or process is applied to the lithium ion battery cathode material, and the main reasons are that (1) the lignin carbon and the nickel oxide in the composite material are large in size, mostly in micron order, the agglomeration phenomenon is still serious, and the problems of volume expansion, low conductivity and poor dispersibility of nickel oxide cannot be effectively alleviated; (2) The lignin carbon has poor structural strength, and is easy to collapse or break in the circulating process, so that the composite material cannot maintain a good structure, and a series of problems of poor circulating stability and the like are caused.

Disclosure of Invention

In order to solve the defects and shortcomings of the prior art, the invention mainly aims to provide a preparation method of a lignin carbon/nickel oxide nano composite material.

Aiming at the problem that the sizes of the lignin carbon and the nickel oxide are larger, according to the physical and chemical properties of lignin, the method firstly further purifies the lignosulfonate by low-concentration sulfuric acid, collects high-solubility components with the sulfonation degree of more than 2.0mmol/g, provides an alkaline solution environment by adjusting the concentration of a carbonate solution, ionizes carboxyl and phenolic hydroxyl in the lignosulfonate, strengthens the electrostatic repulsion action, further develops the three-dimensional network structure of the lignosulfonate, improves the dispersibility, then slowly adds a low-concentration nickel salt solution, enables the nano nickel carbonate to uniformly grow in the three-dimensional network framework of the lignin, effectively reduces the agglomeration of the lignin carbon and nickel oxide particles in the carbonization process, and finally obtains the lignin carbon/nickel oxide nano composite material through carbonization.

Aiming at the problem of poor structural strength of the lignin carbon, on one hand, the method disclosed by the invention starts from the physical and chemical properties of lignin, obtains the lignosulfonate with high sulfonation degree by dilute acid purification, relieves the agglomeration phenomenon of the lignin carbon in the electrochemical reaction process, and further improves the structural stability of the lignin carbon, on the other hand, in the hydrothermal reaction process, the aminobenzene sulfonate and the lignosulfonate are introduced for a crosslinking reaction, so that the three-dimensional network framework of the lignosulfonate is further stabilized, the effective coating and dispersion stabilizing effects of the lignin carbon on nickel oxide particles are facilitated, and the cycle stability of a lithium ion battery is remarkably improved.

The invention also aims to provide the lignin carbon/nickel oxide nanocomposite prepared by the method, wherein the lignin carbon and the nickel oxide exist in a nanoscale, so that the problems of severe volume expansion and poor conductivity when the nickel oxide is used as a lithium ion battery cathode material are effectively solved, and the specific capacity, the cycling stability and the rate capability of the lithium ion battery are improved.

In the invention, the size of the nano lignin carbon is less than 10nm, and the size of the nano nickel oxide is less than 5nm.

The invention further aims to provide application of the lignin carbon/nickel oxide nanocomposite in a lithium ion battery cathode material.

The purpose of the invention is realized by the following technical scheme:

a preparation method of a lignin carbon/nickel oxide nano composite material comprises the following steps:

(1) Carrying out acid treatment on lignosulfonate by using a sulfuric acid solution with the mass concentration of 4-20%, collecting filtrate, adding an ethanol solution with the mass concentration of more than or equal to 50% to precipitate, centrifuging, and drying to obtain purified lignosulfonate with the sulfonation degree of more than 2.0 mmol/g;

(2) Dissolving the purified lignosulfonate obtained in the step (1) in water, then sequentially adding a carbonate solution, a sulfanilate solution, a nickel salt solution and an aldehyde compound solution at the speed of 1-10 mL/min, uniformly mixing, carrying out hydrothermal reaction in a hydrothermal kettle at the temperature of 100-200 ℃ for 1-6 h, filtering, and drying to obtain a lignin/nickel carbonate compound;

(3) Carbonizing the lignin/nickel carbonate composite, then centrifugally washing and drying to obtain the lignin carbon/nickel oxide nano composite material.

Preferably, in the step (2), the mass ratio of the purified lignosulfonate, carbonate, sulfanilate, nickel salt and aldehyde compound is 10g: 1-10 g: 0.5-10 g: 1-10 g:0.5 to 10g.

More preferably, the mass ratio of the purified lignosulfonate, carbonate, sulfanilate, nickel salt and aldehyde compound in the step (2) is 10g: 1-5 g: 0.5-2 g: 1-5 g:0.5 to 2g.

Preferably, the lignosulfonate in the step (1) may be at least one of sodium lignosulfonate, calcium lignosulfonate and magnesium lignosulfonate extracted from the acid pulping red liquor and sulfonated alkali lignin and sulfomethylated alkali lignin obtained by sulfonating/sulfomethylating the alkaline pulping black liquor.

Preferably, the mass ratio of the lignosulfonate to the sulfuric acid solution to the ethanol solution in the step (1) is 1: 2.5-12.5: 2.5 to 5.

Preferably, the mass concentration of the sulfuric acid solution in the step (1) is 5 to 10%.

Preferably, the rotating speed of the centrifugation in the step (1) is more than or equal to 10000rpm, and the time is more than or equal to 10min.

Preferably, the inorganic nickel salt in step (2) is at least one of nickel chloride, nickel nitrate, nickel sulfate and nickel acetate.

Preferably, the carbonate in step (2) is at least one of potassium carbonate, sodium carbonate, ammonium carbonate, potassium bicarbonate, sodium bicarbonate and ammonium bicarbonate.

Preferably, the mass concentration of the solution obtained by dissolving the purified lignosulfonate in the step (2) in water is 10-40%; more preferably 10 to 30%.

Preferably, the mass concentration of the nickel salt solution in the step (2) is 5-20%; more preferably 5 to 10%.

Preferably, the carbonate solution in the step (2) has a mass concentration of 5-20%; more preferably 5 to 10%.

Preferably, the mass concentration of the sulfanilate solution in the step (2) is 10-40%; more preferably 20 to 30%.

Preferably, the aldehyde compound in the step (2) is at least one of formaldehyde, acetaldehyde and propionaldehyde.

Preferably, the mass concentration of the aldehyde compound solution in the step (2) is 20-50%; more preferably 30 to 40%.

Preferably, the adding speed of the step (2) is 2-6 mL/min.

Preferably, the temperature of the hydrothermal treatment in the step (2) is 110-180 ℃ and the time is 1-4 h.

Preferably, the carbonization in the step (3) is performed in a nitrogen or inert gas atmosphere, and the inert gas is at least one of argon and helium.

Preferably, the carbonization procedure in step (3) is as follows: heating to 120-350 ℃ at the speed of 5 ℃/min, preserving heat for 20-60 min, heating to 500-700 ℃ at the speed of 5-10 ℃/min, preserving heat for 0.5-5 h, and cooling to room temperature; more preferably: heating to 250 ℃ at the speed of 5 ℃/min, preserving heat for 30-40 min, heating to 600 ℃ at the speed of 5 ℃/min, preserving heat for 2-3 h, and cooling to room temperature.

Preferably, the centrifugal washing in the step (3) is to soak the carbonized product in water, wash and remove residual pyrolysis products in the carbonized product, and then carry out centrifugal treatment at a rotating speed of more than or equal to 6000rpm for more than or equal to 10min.

Preferably, the drying in the method is at least one of forced air drying, vacuum drying and infrared drying, the drying temperature is higher than 50 ℃, and the drying time is more than or equal to 4 hours.

The lignin carbon/nickel oxide nano composite material prepared by the method.

The lignin carbon/nickel oxide nano composite material is applied to the fields of lithium ion battery cathode materials, supercapacitors and photoelectrocatalysis.

The present invention will be described in more detail below.

(1) And (2) carrying out acid treatment and purification on the lignosulfonate by using a sulfuric acid solution with the mass concentration of 1-20%, collecting filtrate, adding an ethanol solution with the mass concentration of more than or equal to 50% to separate out a precipitate, and carrying out centrifugal separation and drying on the precipitate to obtain the purified lignosulfonate with the sulfonation degree of more than 2.0 mmol/g.

According to the physical and chemical properties of lignin, low-concentration sulfuric acid is used for purifying lignosulfonate to remove components with the sulfonation degree lower than 2.0mmol/g, filtrate is collected, ethanol solution with the mass concentration of more than or equal to 50% is added to separate out lignosulfonate precipitate, water-soluble inorganic salt and the like are removed, and the solid product obtained after the precipitate is dried is the purified lignosulfonate with the sulfonation degree of more than 2.0 mmol/g.

The concentration of the sulfuric acid solution in the step needs to be controlled, if the mass concentration is less than 5%, the purification effect is poor, lignosulfonate with the sulfonation degree of less than 2.0mmol/g is difficult to remove, and the obtained purified lignosulfonate has insufficient high water solubility, so that the lignosulfonate cannot be uniformly dispersed with nickel carbonate in the solution, and further small-size nano lignin carbon and nano nickel oxide are difficult to form in the carbonization process; if the mass concentration is more than 10 percent, the cost is higher.

(2) Preparing purified lignosulfonate, carbonate, nickel salt, sulfanilate and aldehyde compound aqueous solution with certain mass concentration, sequentially and slowly adding carbonate solution, sulfanilate solution, nickel salt solution and aldehyde compound solution into the purified lignosulfonate solution, stirring for more than 20min, then placing at 100-200 ℃ for hydrothermal reaction for 1-6 h, filtering and drying to obtain lignin/nickel carbonate compound;

the step is to provide an alkaline environment through carbonate hydrolysis, further promote the extension of a three-dimensional network structure of purified lignosulfonate, then add sulfanilate, further promote the dispersion of nickel carbonate in a hydrothermal process, and through hydrothermal reaction, sulfanilate can also generate crosslinking with an aldehyde compound and the purified lignosulfonate, so that the structural strength of a three-dimensional network framework of lignin is further stabilized, and finally a small-size lignin/nickel carbonate compound is obtained.

In the step, the carbonate solution needs to be slowly added into the purified lignosulfonate solution to be fully hydrolyzed and provide an alkaline environment, then the sulfanilate solution is slowly added, and finally nickel ions are slowly introduced to generate the small-size nickel carbonate with good dispersion. If nickel ions are introduced first and then the carbonate solution is added, an alkaline environment cannot be provided during the growth of nickel carbonate crystal nucleus, so that the three-dimensional network skeleton of the lignosulfonate is difficult to expand, and agglomeration is caused. Stirring was carried out during this period to disperse the lignin/nickel carbonate complex uniformly in the mixed solution.

The concentration of the nickel salt solution and the carbonate solution is strictly controlled in the step, and the nickel carbonate cannot be directly used. If the concentration of the nickel salt and the carbonate solution is too high, a large amount of agglomerated large-particle nickel carbonate solids can be generated in the solution, and the lignosulfonate cannot coat the nickel carbonate, so that the composite material is unstable in structure and poor in electrochemical performance; however, the nickel carbonate and lignin are not uniformly dispersed when the nickel carbonate is directly used, and good electrochemical performance cannot be obtained.

In the step, the mass concentrations of the sulfanilate solution and the aldehyde compound are also strictly controlled, if the mass concentrations are too high, the condensation of the lignosulfonate is excessive in the hydrothermal process, the structural stability of the lignosulfonate/nickel carbonate compound is damaged, and the local agglomeration or exposure is caused; if the mass concentration is too low, the lignin sulfonate is not condensed thoroughly in the hydrothermal process, which is not beneficial to improving the lignin structural strength.

In the step, the hydrothermal reaction can further nucleate the primary-grown nickel carbonate crystal grains and compound the crystal grains with lignosulfonate, and simultaneously, the sulfanilate and the lignosulfonate are further crosslinked to improve the strength of a three-dimensional network framework of lignin. The step needs to control the temperature and time of the hydrothermal reaction, the temperature is too high, the time is too long, the nickel carbonate crystal grows excessively, serious agglomeration occurs, the energy consumption is large, and the production cost is increased; if the temperature is too low and the time is too short, the nickel carbonate crystal nucleus cannot grow to be stable, and meanwhile, the lignin is not completely crosslinked, so that the composite material has poor structural strength and is easy to collapse or break in the carbonization process.

(3) And (3) carbonizing the lignin/nickel carbonate composite obtained in the step (2), washing, centrifuging and drying to obtain the lignin carbon/nickel oxide nano composite material.

In the step, the carbonization atmosphere is nitrogen atmosphere, and other inert gases such as argon, helium and the like can be replaced. The carbonization temperature is required to be within 500-700 ℃, the time is within 0.5-5 h, if the temperature is too low and the time is too short, the lignin is incompletely carbonized, a large number of oxygen-containing functional groups exist on the surface, and side reactions are easy to occur in the charging and discharging processes, so that the lithium storage performance of the composite material is reduced; if the temperature is too high and the time is too long, on one hand, the energy consumption is too high, the production cost is obviously increased, on the other hand, the lignin carbon structure is unstable, and the circulation stability of the composite material is reduced.

In the invention, the size of the lignin carbon/nickel oxide nano composite material is less than 10nm, and the lignin carbon/nickel oxide nano composite material can be applied to the fields of lithium ion battery cathode materials, supercapacitors and photoelectrocatalysis.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) The particle size of the lignin carbon/nickel oxide nano composite material prepared by the invention is less than 10nm, the structure is more regular and ordered, the particle size of the nano nickel oxide serving as an electrochemical active component is less than 5nm, the distribution of the nano nickel oxide in a lignin carbon skeleton is more uniform, the lignin nano carbon can effectively coat the nickel oxide to inhibit the volume expansion effect of the nickel oxide, and the higher conductivity of the lignin carbon compared with the nickel oxide can also effectively improve the overall electronic diffusion rate of the composite material, so that excellent cycle performance and rate capability are obtained. In addition, the lignin carbon in the composite material has higher structural strength, is not easy to break and collapse in electrochemical reaction, and is beneficial to the circulation stability of the composite material. As a lithium ion battery cathode material, compared with pure nano nickel oxide, the lithium ion battery cathode material has better cycle performance and rate capability, and has good application prospect.

(2) In the preparation process of the lignin carbon/nickel oxide nano composite material, lignosulfonate is used as a carbon source, nickel salt is used as a nickel source, good coating of the lignin nano carbon on the nano nickel oxide is realized, the raw material is a renewable resource which is rich in reserves, low in price and easy to obtain, the preparation process is green, simple and environment-friendly, the resource utilization of papermaking black liquor or biorefinery waste can be realized, the resource is saved, the environment is protected, and the application prospect is wide.

Drawings

FIG. 1 is a constant current charge and discharge diagram of the lignin carbon/nickel oxide nanocomposite prepared in example 1 of the present invention.

FIG. 2 is a graph of the rate capability of the lignin carbon/nickel oxide nanocomposite prepared in example 1 of the present invention.

FIG. 3 is an SEM image of a lignin carbon/nickel oxide nanocomposite prepared according to example 1 of the present invention, wherein the upper left panel is a particle size distribution diagram of the composite.

FIG. 4 is a TEM image of a lignin char/nickel oxide nanocomposite obtained in example 1 of the present invention.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.

Those who do not specify specific conditions in the examples of the present invention follow conventional conditions or conditions recommended by the manufacturer. The raw materials, reagents and the like which are not indicated for manufacturers are all conventional products which can be obtained by commercial purchase.

Example 1

Taking 500g of sulfuric acid solution with the mass concentration of 10%, adding 100g of sodium lignosulfonate powder while stirring, and then filtering to obtain a filtrate. And adding 500g of ethanol solution with the mass concentration of 50% into the obtained filtrate while stirring, centrifuging at the rotating speed of 10000rpm for 10min, pouring out supernatant liquid, and transferring the centrifuged precipitate into an infrared drying oven at 50 ℃ for drying for 24h to obtain the purified sodium lignosulfonate with the sulfonation degree of more than 2.0 mmol/g.

Preparing 100g of the purified sodium lignosulfonate solution with the mass concentration of 10%, 30g of the nickel chloride solution with the mass concentration of 10%, 30g of the sodium carbonate solution with the mass concentration of 10%, 3g of the sodium sulfanilate solution with the mass concentration of 30% and 3g of the formaldehyde solution with the mass concentration of 40%, and slowly dripping the sodium carbonate solution, the sodium sulfanilate solution, the nickel chloride solution and the formaldehyde solution into the purified sodium lignosulfonate solution at the speed of 2mL/min by using a peristaltic pump, wherein the stirring is carried out while dripping. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 2h in an air atmosphere of 120 ℃, filtering, and drying the precipitate to obtain the lignin/nickel carbonate compound.

And transferring the prepared lignin/nickel carbonate composite into a carbonization furnace, raising the temperature to 250 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, keeping the temperature for 30min, raising the temperature to 600 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 2h, cooling the carbonization product to room temperature, soaking the carbonization product in deionized water for washing, centrifuging the carbonization product at the rotating speed of 10000rpm for 10min, pouring out supernatant liquid, transferring the centrifuged precipitate into an infrared oven at 50 ℃ and drying the centrifuged precipitate for 24h to prepare the lignin carbon/nickel oxide nanocomposite.

Example 2

Adding 250g of 20% sulfuric acid solution into 100g of sodium lignosulfonate powder while stirring, and filtering to obtain a filtrate. And adding 416.7g of ethanol solution with the mass concentration of 60% into the obtained filtrate while stirring, centrifuging at the rotating speed of 10000rpm for 15min, pouring out supernatant liquid, transferring the centrifuged precipitate into an infrared drying oven at 50 ℃ for drying for 24h to obtain the purified sodium lignosulfonate with the sulfonation degree of more than 2.0 mmol/g.

Preparing 25g of the purified sodium lignosulfonate solution with the mass concentration of 40%, 25g of the nickel nitrate solution with the mass concentration of 20%, 25g of the sodium bicarbonate solution with the mass concentration of 20%, 5g of the sodium sulfanilate solution with the mass concentration of 40% and 4g of the formaldehyde solution with the mass concentration of 50%, and slowly and dropwise adding the sodium bicarbonate solution, the sodium sulfanilate solution, the nickel nitrate solution and the formaldehyde solution into the purified sodium lignosulfonate solution at the speed of 10mL/min by using a peristaltic pump in sequence while stirring. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 6h in an air atmosphere of 200 ℃, filtering, and drying the precipitate to obtain the lignin/nickel carbonate compound.

And transferring the prepared lignin/nickel carbonate composite into a carbonization furnace, raising the temperature to 350 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, keeping for 60min, raising the temperature to 700 ℃ at the heating rate of 10 ℃/min, keeping for 5h, cooling to room temperature, soaking a carbonization product into deionized water for washing, centrifuging at the rotating speed of 10000rpm for 10min, pouring out supernatant liquid, transferring the centrifuged precipitate into a 50 ℃ infrared oven, and drying for 24h to obtain the lignin carbon/nickel oxide nanocomposite.

Example 3

1250g of a 4% by mass sulfuric acid solution was added to 100g of magnesium lignosulfonate powder while stirring, and then filtered to obtain a filtrate. 357.1g of ethanol solution with the mass concentration of 70 percent is taken and added into the obtained filtrate while stirring, then the mixture is centrifuged at the rotating speed of 12000rpm for 10min, the supernatant liquid is poured off, and the centrifuged precipitate is transferred into an infrared drying oven with the temperature of 50 ℃ for drying for 24h, thus obtaining the purified magnesium lignosulfonate with the sulfonation degree of more than 2.0 mmol/g.

Preparing 100g of the purified magnesium lignosulfonate solution with the mass concentration of 10%, 20g of the nickel sulfate solution with the mass concentration of 5%, 20g of the potassium carbonate solution with the mass concentration of 5%, 5g of the sodium sulfanilate solution with the mass concentration of 10% and 2.5g of the acetaldehyde solution with the mass concentration of 20%, and slowly and dropwise adding the potassium carbonate solution, the sodium sulfanilate solution, the nickel sulfate solution and the acetaldehyde solution into the purified magnesium lignosulfonate solution at the speed of 2mL/min by using a peristaltic pump in sequence while stirring. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 1h in an air atmosphere of 100 ℃, filtering, and drying the precipitate to obtain the lignin/nickel carbonate compound.

And transferring the prepared lignin/nickel carbonate composite into a carbonization furnace, raising the temperature to 120 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, keeping for 20min, raising the temperature to 500 ℃ at the heating rate of 5 ℃/min, keeping for 0.5h, cooling to room temperature, soaking a carbonized product into deionized water for washing, centrifuging at the rotating speed of 10000rpm for 10min, pouring out supernatant liquor, and transferring the centrifuged precipitate into a 50 ℃ infrared oven for drying for 24h to prepare the lignin carbon/nickel oxide nanocomposite.

Example 4

Taking 500g of 10% sulfuric acid solution, adding 100g of calcium lignosulfonate powder while stirring, and filtering to obtain a filtrate. 357.1g of ethanol solution with the mass concentration of 70 percent is taken and added into the obtained filtrate while stirring, then the mixture is centrifuged for 10min at the rotating speed of 11000rpm, the supernatant liquid is poured off, and the centrifuged precipitate is transferred into an infrared drying oven with the temperature of 50 ℃ to be dried for 24h, so as to obtain the purified calcium lignosulphonate with the sulfonation degree of more than 2.0 mmol/g.

Preparing 33.3g of the purified calcium lignosulfonate solution with the mass concentration of 30%, 50g of a nickel acetate solution with the mass concentration of 10%, 50g of a potassium bicarbonate solution with the mass concentration of 10%, 6.7g of a sodium sulfanilate solution with the mass concentration of 30% and 5g of a propionaldehyde solution with the mass concentration of 40%, and slowly and dropwise adding the potassium bicarbonate solution, the sodium sulfanilate solution, the nickel acetate solution and the propionaldehyde solution into the purified calcium lignosulfonate solution at the speed of 6mL/min by using a peristaltic pump while stirring. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 4h in an air atmosphere of 180 ℃, filtering, and drying the precipitate to obtain the lignin/nickel carbonate compound.

And transferring the prepared lignin/nickel carbonate composite into a carbonization furnace, raising the temperature to 250 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, keeping the temperature for 40min, raising the temperature to 650 ℃ at the heating rate of 10 ℃/min, keeping the temperature for 1h, cooling the carbonization product to room temperature, soaking the carbonization product in deionized water for washing, centrifuging the carbonization product at the rotating speed of 10000rpm for 10min, pouring out supernatant liquid, transferring the centrifuged precipitate into an infrared oven at 50 ℃ and drying the centrifuged precipitate for 24h to prepare the lignin carbon/nickel oxide nanocomposite.

Example 5

625g of sulfuric acid solution with the mass concentration of 8 percent is taken, 100g of sulfonated alkali lignin powder is added while stirring, and then the filtrate is obtained by filtration. And adding 500g of ethanol solution with the mass concentration of 70% into the obtained filtrate while stirring, centrifuging at the rotating speed of 10000rpm for 20min, pouring out the supernatant, transferring the centrifuged precipitate into an infrared drying oven at 50 ℃ for drying for 24h to obtain the purified sulfonated alkali lignin with the sulfonation degree of more than 2.0 mmol/g.

Preparing 100g of the purified sulfonated alkali lignin solution with the mass concentration of 10%, 10g of the nickel chloride solution with the mass concentration of 10%, 10g of the ammonium carbonate solution with the mass concentration of 10%, 2.5g of the sodium sulfanilate solution with the mass concentration of 20% and 1.67g of the formaldehyde solution with the mass concentration of 30%, and slowly dropwise adding the ammonium carbonate solution, the ammonium sulfanilate solution, the nickel chloride solution and the formaldehyde solution into the purified sulfonated alkali lignin solution at the speed of 5mL/min by using a peristaltic pump in sequence while stirring. Stirring for more than 20min, transferring the mixed solution to a hydrothermal kettle, heating for 3h in an air atmosphere at 110 ℃, filtering, and drying the precipitate to obtain the lignin/nickel carbonate compound.

Transferring the prepared lignin/nickel carbonate composite into a carbonization furnace, raising the temperature to 300 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, keeping the temperature for 30min, raising the temperature to 550 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 3h, cooling the carbonization product to room temperature, soaking the carbonization product in deionized water for washing, centrifuging the carbonization product at the rotating speed of 10000rpm for 10min, pouring out supernatant liquid, transferring the centrifuged precipitate into an infrared oven at 50 ℃ and drying the centrifuged precipitate for 24h to prepare the lignin carbon/nickel oxide nanocomposite.

Example 6

Taking 500g of sulfuric acid solution with the mass concentration of 10%, adding 100g of sulfomethylated alkali lignin powder while stirring, and filtering to obtain filtrate. And adding 500g of 50% ethanol solution into the obtained filtrate while stirring, centrifuging at 10000rpm for 10min, pouring out the supernatant, transferring the centrifuged precipitate into an infrared drying oven at 50 ℃ for drying for 24h to obtain the purified sulfomethylated alkali lignin with the sulfonation degree of more than 2.0 mmol/g.

Preparing 50g of the purified sulfomethylated alkali lignin solution with the mass concentration of 20%, 13.3g of a nickel chloride solution with the mass concentration of 15%, 13.3g of an ammonium bicarbonate solution with the mass concentration of 15%, 5g of a sodium sulfanilate solution with the mass concentration of 25% and 3.57g of a formaldehyde solution with the mass concentration of 35%, and slowly dropwise adding the ammonium bicarbonate solution, the ammonium sulfanilate solution, the nickel chloride solution and the formaldehyde solution into the purified sulfomethylated alkali lignin solution at the speed of 3mL/min by using a peristaltic pump in sequence while stirring. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 2h in the air atmosphere of 150 ℃, filtering, and drying the precipitate to obtain the lignin/nickel carbonate compound.

And transferring the prepared lignin/nickel carbonate composite into a carbonization furnace, raising the temperature to 250 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, keeping the temperature for 35min, raising the temperature to 600 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 2h, cooling the carbonization product to room temperature, soaking the carbonization product in deionized water for washing, centrifuging the carbonization product at the rotating speed of 10000rpm for 10min, pouring out supernatant liquid, transferring the centrifugal precipitate into an infrared oven at 50 ℃ and drying the centrifugal precipitate for 24h to prepare the lignin carbon/nickel oxide nanocomposite.

Comparative example 1 (using pure nickel oxide directly) demonstrates the effective coating of lignin-free carbon, and the pure phase nano nickel oxide is easy to agglomerate.

Preparing 30g of a 10% nickel chloride solution and 30g of a 10% sodium carbonate solution, and slowly adding the nickel chloride solution into the sodium carbonate solution at a speed of 2mL/min by using a peristaltic pump while stirring. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 2h in an air atmosphere of 120 ℃, filtering, and drying the precipitate to obtain the nickel carbonate.

And transferring the prepared nickel carbonate into a carbonization furnace, raising the temperature to 250 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, keeping the temperature for 30min, raising the temperature to 600 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 2h, cooling the temperature to room temperature, soaking a carbonized product into deionized water for washing, centrifuging the carbonized product at the rotating speed of 10000rpm for 10min, pouring out supernatant liquid, transferring the centrifuged precipitate into a 50 ℃ infrared oven, and drying the centrifuged precipitate for 24h to obtain the nano nickel oxide material.

Comparative example 2 (nickel carbonate is directly used) proves that nickel carbonate is not dispersed uniformly in the preparation process of firstly dissolving nickel salt and then precipitating, lignin cannot be effectively coated, and nickel oxide particles generated after carbonization are large and easy to agglomerate.

500g of a 10% sulfuric acid solution was added to 100g of sodium lignosulfonate powder while stirring, and then the mixture was filtered to obtain a filtrate. And adding 500g of 50% ethanol solution into the obtained filtrate while stirring, centrifuging at 10000rpm for 10min, pouring out the supernatant, and transferring the centrifuged precipitate into an infrared drying oven at 50 ℃ for drying for 24h to obtain the purified sodium lignosulfonate with the sulfonation degree of more than 2.0 mmol/g.

Preparing 100g of the purified sodium lignosulfonate solution with the mass concentration of 10%, 30g of the nickel carbonate suspension with the mass concentration of 10%, 3g of the sodium sulfanilate solution with the mass concentration of 30% and 3g of the formaldehyde solution with the mass concentration of 40%, and slowly dripping the nickel carbonate suspension, the sodium sulfanilate solution and the formaldehyde solution into the purified sodium lignosulfonate solution at the speed of 2mL/min by using a peristaltic pump while stirring. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 2h in an air atmosphere of 120 ℃, filtering, and drying the precipitate to obtain the lignin/nickel carbonate compound.

Comparative example 3 (removing all nickel oxide, leaving only lignin char) demonstrates that it is difficult to obtain excellent electrochemical performance with lignin char alone.

And transferring the prepared lignin/nickel carbonate compound into a carbonization furnace, raising the temperature to 250 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, keeping the temperature for 30min, raising the temperature to 600 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 2h, cooling the carbonization product to room temperature, soaking the carbonization product into a sulfuric acid solution with the mass concentration of 50%, washing, centrifuging the carbonization product at the rotating speed of 10000rpm for 10min, pouring out supernatant liquor, transferring the centrifuged precipitate into a 50 ℃ infrared oven, and drying the centrifuged precipitate for 24h to obtain the nano lignin carbon material.

Comparative example 4 (unpurified sodium lignosulfonate, using sodium sulfanilate and an aldehyde compound), which proves the importance of the sulfonation degree of more than 2.0mmol/g, proves that the unpurified sodium lignosulfonate cannot be well dispersed in the solution, so that the generated nickel carbonate and lignin are not uniformly dispersed, and the carbonized lignin carbon and nickel oxide particles are large and seriously agglomerated.

Preparing 100g of 10 mass percent unrefined sodium lignosulfonate solution, 30g of 10 mass percent nickel chloride solution, 30g of 10 mass percent sodium carbonate solution, 3g of 30 mass percent sodium sulfanilate solution and 3g of 40 mass percent formaldehyde solution, and slowly dripping the sodium carbonate solution, the sodium sulfanilate solution, the nickel chloride solution and the formaldehyde solution into the unrefined sodium lignosulfonate solution at the speed of 2mL/min by using a peristaltic pump while stirring. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 2h in an air atmosphere of 120 ℃, filtering, and drying the precipitate to obtain the lignin/nickel carbonate compound.

Comparative example 5 (purified sodium lignosulfonate, without sodium sulfanilate and aldehyde compounds), it is proved that the cross-linking of sodium sulfanilate and lignin can improve the structural strength, and the carbonized lignin carbon/nickel oxide nano composite material can be formed, but the structural strength is not enough.

500g of a 10% sulfuric acid solution was added to 100g of sodium lignosulfonate powder while stirring, and then the mixture was filtered to obtain a filtrate. And adding 500g of ethanol solution with the mass concentration of 50% into the obtained filtrate while stirring, centrifuging at the rotating speed of 10000rpm for 10min, pouring out supernatant liquid, and transferring the centrifuged precipitate into an infrared drying oven at 50 ℃ for drying for 24h to obtain the purified sodium lignosulfonate with the sulfonation degree of more than 2.0 mmol/g.

Preparing 100g of the purified sodium lignosulfonate solution with the mass concentration of 10%, 30g of the nickel chloride solution with the mass concentration of 10% and 30g of the sodium carbonate solution with the mass concentration of 10%, and slowly dripping the sodium carbonate solution and the nickel chloride solution into the purified sodium lignosulfonate solution at the speed of 2mL/min by using a peristaltic pump while stirring. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 2h in an air atmosphere of 120 ℃, filtering, and drying the precipitate to obtain the lignin/nickel carbonate compound.

Comparative example 6 (purification of sodium lignosulfonate, use of sodium sulfanilate, use of aldehyde compounds condensation under atmospheric pressure), it is demonstrated that the compound obtained by conventional crosslinking can be a lignin with increased molecular weight, but can not effectively coat nickel carbonate, resulting in nickel carbonate agglomeration.

Preparing 100g of the purified sodium lignosulfonate solution with the mass concentration of 10%, 30g of the nickel chloride solution with the mass concentration of 10%, 30g of the sodium carbonate solution with the mass concentration of 10%, 3g of the sodium sulfanilate solution with the mass concentration of 30% and 3g of the formaldehyde solution with the mass concentration of 40%, and slowly dripping the sodium carbonate solution, the sodium sulfanilate solution, the nickel chloride solution and the formaldehyde solution into the purified sodium lignosulfonate solution at the speed of 2mL/min by using a peristaltic pump, wherein the stirring is carried out while dripping. Stirring for more than 20min, transferring the mixed solution into a three-neck flask, placing the three-neck flask in an oil bath kettle at 120 ℃, heating and stirring for 2h, filtering, and drying the precipitate to obtain the lignin/nickel carbonate compound.

Comparative example 7 (sodium lignosulfonate purified, sodium sulfanilate used, aldehyde compound not used) shows that the structural strength cannot be improved by using sodium sulfanilate alone.

Preparing 100g of the purified sodium lignosulfonate solution with the mass concentration of 10%, 30g of the nickel chloride solution with the mass concentration of 10%, 30g of the sodium carbonate solution with the mass concentration of 10% and 3g of the sodium sulfanilate solution with the mass concentration of 30%, and slowly dripping the sodium carbonate solution, the sodium sulfanilate solution and the nickel chloride solution into the purified sodium lignosulfonate solution at the speed of 2mL/min by using a peristaltic pump while stirring. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 2h in an air atmosphere of 120 ℃, filtering, and drying the precipitate to obtain the lignin/nickel carbonate compound.

Comparative example 8: changing the order of addition proved to be beneficial for nickel carbonate nucleation in the correct order of addition, and sodium carbonate had to be added first to provide an alkaline environment.

Taking 500g of sulfuric acid solution with the mass concentration of 10%, adding 100g of sodium lignosulfonate powder while stirring, and then filtering to obtain a filtrate. And adding 500g of 50% ethanol solution into the obtained filtrate while stirring, centrifuging at 10000rpm for 10min, pouring out the supernatant, and transferring the centrifuged precipitate into an infrared drying oven at 50 ℃ for drying for 24h to obtain the purified sodium lignosulfonate with the sulfonation degree of more than 2.0 mmol/g.

Preparing 100g of the purified sodium lignosulfonate solution with the mass concentration of 10%, 30g of the nickel chloride solution with the mass concentration of 10%, 30g of the sodium carbonate solution with the mass concentration of 10%, 3g of the sodium sulfanilate solution with the mass concentration of 30% and 3g of the formaldehyde solution with the mass concentration of 40%, and slowly and dropwise adding the nickel chloride solution, the sodium sulfanilate solution, the formaldehyde solution and the sodium carbonate solution into the purified sodium lignosulfonate solution at the speed of 2mL/min by using a peristaltic pump in sequence while stirring. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 2h in an air atmosphere of 120 ℃, filtering, and drying the precipitate to obtain the lignin/nickel carbonate compound.

And transferring the prepared lignin/nickel carbonate composite into a carbonization furnace, raising the temperature to 250 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, keeping the temperature for 30min, raising the temperature to 600 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 2h, cooling the carbonization product to room temperature, soaking the carbonization product in deionized water for washing, centrifuging the carbonization product at the rotating speed of 10000rpm for 10min, pouring out supernatant liquid, transferring the centrifugal precipitate into an infrared oven at 50 ℃ and drying the centrifugal precipitate for 24h to prepare the lignin carbon/nickel oxide nanocomposite.

Comparative example 9 (sodium lignosulfonate purified, sodium sulfanilate not used, and aldehyde compound used) proves that only the aldehyde compound is used to generate certain crosslinking, and meanwhile, certain agglomeration is accompanied, so that the structural strength cannot be effectively improved.

Preparing 100g of the purified sodium lignosulfonate solution with the mass concentration of 10%, 30g of the nickel chloride solution with the mass concentration of 10%, 30g of the sodium carbonate solution with the mass concentration of 10% and 3g of the formaldehyde solution with the mass concentration of 40%, fully stirring, and then slowly dropwise adding the sodium carbonate solution, the nickel chloride solution and the formaldehyde solution into the purified sodium lignosulfonate solution at the speed of 2mL/min by using a peristaltic pump in sequence while stirring. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 2h in an air atmosphere of 120 ℃, filtering, and drying the precipitate to obtain the lignin/nickel carbonate compound.

Comparative example 10 (sodium hydroxide is used to provide an alkaline environment), which proves that alkaline substances such as sodium hydroxide or ammonia water can improve the dispersibility of lignosulfonate, but water vapor released in the carbonization process by using nickel hydroxide generated by combining nickel ions as a template agent cannot achieve good effects of pore forming and lignin carbon agglomeration inhibition, the obtained lignin carbon/nickel oxide nano composite material has certain agglomeration, and the outer layer coated lignin carbon layer has uneven thickness.

Preparing 100g of the purified sodium lignosulfonate solution with the mass concentration of 10%, 30g of the nickel chloride solution with the mass concentration of 10%, 30g of the sodium hydroxide solution with the mass concentration of 10%, 3g of the sodium sulfanilate solution with the mass concentration of 30% and 3g of the formaldehyde solution with the mass concentration of 40%, and slowly and dropwise adding the sodium hydroxide solution, the nickel chloride solution, the sodium sulfanilate solution and the formaldehyde solution into the purified sodium lignosulfonate solution at the speed of 2mL/min by using a peristaltic pump in sequence while stirring. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 2h in an air atmosphere of 120 ℃, filtering, and drying the precipitate to obtain the lignin/nickel hydroxide compound.

Transferring the prepared lignin/nickel hydroxide composite into a carbonization furnace, raising the temperature to 250 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, keeping the temperature for 30min, raising the temperature to 600 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 2h, cooling the carbonization product to room temperature, soaking the carbonization product in deionized water for washing, centrifuging the carbonization product at the rotating speed of 10000rpm for 10min, pouring out supernatant liquid, transferring the centrifuged precipitate into an infrared oven at 50 ℃ and drying the centrifuged precipitate for 24h to prepare the lignin carbon/nickel oxide nanocomposite.

Comparative example 11 (using potassium oxalate to provide an alkaline environment) proves that oxalate hydrolysis is relatively weak in alkalinity and may not have the same effect on the development of a three-dimensional network structure of lignosulfonate as carbonate, and carbon monoxide and carbon dioxide which are released in a large amount in a carbonization process by combining nickel ions to generate nickel oxalate as a template can damage the material structure, so that the structural strength is reduced.

Preparing 100g of the purified sodium lignosulfonate solution with the mass concentration of 10%, 30g of the nickel chloride solution with the mass concentration of 10%, 30g of the potassium oxalate solution with the mass concentration of 10%, 3g of the sodium sulfanilate solution with the mass concentration of 30% and 3g of the formaldehyde solution with the mass concentration of 40%, fully stirring, and then slowly dropwise adding the potassium oxalate solution, the nickel chloride solution, the sodium sulfanilate solution and the formaldehyde solution into the purified sodium lignosulfonate solution at the speed of 2mL/min by using a peristaltic pump in sequence while stirring. Stirring for more than 20min, transferring the mixed solution into a hydrothermal kettle, heating for 2h in an air atmosphere of 120 ℃, filtering, and drying the precipitate to obtain the lignin/nickel hydroxide compound.

And transferring the prepared lignin/nickel hydroxide composite into a carbonization furnace, raising the temperature to 250 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, keeping the temperature for 30min, raising the temperature to 600 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 2h, cooling the carbonization product to room temperature, soaking the carbonization product in deionized water for washing, centrifuging the carbonization product at the rotating speed of 10000rpm for 10min, pouring out supernatant liquid, transferring the centrifugal precipitate into an infrared oven at 50 ℃ and drying the centrifugal precipitate for 24h to prepare the lignin carbon/nickel oxide nanocomposite.

The morphology and size of the samples of the invention were tested by field emission scanning electron microscopy (SEM, hitachi SU 8220) and high resolution field emission transmission electron microscopy (HRTEM, JEOL JEM-2100F, 200kV) equipped with an energy spectrometer (ThermoFisher Scientific, NORAN System 7).

The battery assembly adopts half battery assembly, and the model is CR2032. The positive electrode material comprises 80wt% of active substance, 10wt% of conductive carbon black and 10wt% of polyvinylidene fluoride (PVDF), and is coated by adopting N-methyl-2-pyrrolidone (NMP) as a solvent, wherein the active substance is the lignin carbon/nickel oxide nano-material prepared in the above examples and comparative examplesA rice composite material. The lithium sheet is used as a counter electrode, and the electrolyte is 1mol/L LiPF ₆ Ethylene Carbonate (EC), ethyl Methyl Carbonate (EMC), and dimethyl carbonate (DMC) as solutes in a volume ratio of 1. The entire assembly process of the lithium ion half cell was performed in an argon protected glove box (Super 1220/750, mikruina). The constant current charge/discharge performance test of the battery is carried out by using a Newware battery performance test system in a voltage range of 0.01-3V and at a current density of 200mA/g, and the rate performance test is completed at current densities of 50mA/g, 100mA/g, 250mA/g, 500mA/g and 1000 mA/g.

The lignin carbon/nickel oxide nanocomposite prepared in example 1 was applied to a lithium ion battery negative electrode material and subjected to material characterization and electrochemical tests, and the results are shown in table 1 and fig. 1 to 4.

Table 1 is a comparison of the cycling performance of the lignin carbon/nickel oxide nanocomposites prepared in the above examples with the samples prepared in the comparative examples described below.

TABLE 1 circulation Properties of Lignin carbon/Nickel oxide nanocomposites with comparative examples 1-11

Table 1 illustrates:

the lignin carbon/nickel oxide nanocomposite prepared in the embodiment 1 has a specific discharge capacity of 1065mAh/g after 100 cycles at a current density of 200mA/g, is good in cycle stability and is significantly superior to similar materials, and the cycle performance of all samples in the embodiment is superior to that of other samples in comparative examples, so that the lignin carbon/nickel oxide nanocomposite is mainly benefited from the advantages that the particle size is small, the nano nickel oxide is well coated by the nano lignin carbon, the excellent structural strength of a nano lignin carbon skeleton is achieved, and the lignin carbon and the nickel oxide play a synergistic effect.

The cycle performance data of the comparative example samples in the table 1 show that after 100 cycles at 200mA/g, the pure nickel oxide of the comparative example 1 is still easy to expand and agglomerate due to no coating of lignin carbon, and the specific discharge capacity of the pure nickel oxide is only 101mAh/g; in the comparative example 2, nickel carbonate is directly used, so that nickel carbonate and lignin are not uniformly dispersed, the lignin cannot be effectively coated, and nickel oxide particles generated by carbonization are large and are easy to agglomerate, so that the discharge specific capacity is only 673mAh/g; comparative example 3 the specific discharge capacity was only 582mAh/g due to the removal of all nickel oxide by acid etching, only lignin carbon remaining, lacking the capacity contribution of nickel oxide; comparative example 4 because of using the sodium lignosulfonate not purified, its sulfonation degree is less than 2.0mmol/g, can't disperse well in solution, cause nickel carbonate and lignin that produce to disperse unevenly, the lignin charcoal and nickel oxide particle size that the carbonization produces are all great, agglomerate seriously, its specific discharge capacity is only 747mAh/g; in the comparative example 5, sodium sulfanilate, aldehyde compounds and sodium lignosulfonate are not used for crosslinking, so that the structure strength of the formed lignin carbon/nickel oxide nano composite material after carbonization is insufficient, and the specific discharge capacity is 822mAh/g; in the comparative example 6, the sodium lignosulfonate and the sodium sulfanilate are subjected to condensation crosslinking under normal pressure, so that the molecular weight of lignin is increased, the three-dimensional network framework of the lignin cannot be stabilized, the effective coating, dispersion and stabilization effects on the nickel carbonate are difficult to exert, the nickel carbonate is agglomerated, and the discharge specific capacity of the nickel carbonate is only 709mAh/g; in the comparative example 7, as the aldehyde compound is not used, only sodium sulfanilate cannot be condensed and crosslinked with sodium lignosulfonate, so that the structural strength of the carbon lignin/nickel oxide nano composite material cannot be improved, and the specific discharge capacity of the carbon lignin/nickel oxide nano composite material is 834mAh/g; in the comparative example 8, the charging sequence is changed, sodium carbonate is not firstly added to provide an alkaline environment, so that the three-dimensional network skeleton of sodium lignosulfonate is not unfolded, the dispersibility is poor, the generated nickel carbonate is limited in the three-dimensional network skeleton, the uniform particle size of the lignin carbon and the nickel oxide obtained after carbonization is larger, the agglomeration is serious, and the specific discharge capacity is only 692mAh/g. In the comparative example 9, sodium sulfanilate is not used, only the aldehyde compound and sodium lignosulfonate are incompletely condensed and crosslinked, the improvement on the structural strength of the carbon lignin/nickel oxide nano composite material is small, in addition, the dispersion stabilizing effect of the sodium sulfanilate is lacked, the lignin is agglomerated to a certain degree, and the specific discharge capacity is 837mAh/g. In comparative example 10, sodium hydroxide is used to provide an alkaline environment, and although the dispersibility of sodium lignosulfonate can be improved, nickel hydroxide is generated by combining with nickel ions at this time, and water vapor released in the carbonization process as a template agent cannot effectively form pores and inhibit lignin carbon agglomeration, so that the obtained lignin carbon/nickel oxide nanocomposite has a certain agglomeration structure, a surface pore structure is too few, lithium storage active sites are lacked, and the specific discharge capacity is only 498mAh/g. Comparative example 11 since potassium oxalate is used to provide an alkaline environment, the solution obtained by hydrolysis is relatively weak in alkalinity, which is not favorable for effective development of the three-dimensional network skeleton structure of sodium lignosulfonate, and in addition, nickel oxalate generated by combination of nickel oxalate and nickel ions is used as a template agent to release excessive carbon monoxide and carbon dioxide gas in the carbonization process, so that the structure of the lignin carbon is damaged, the structural strength of the lignin carbon/nickel oxide nano composite material is reduced, and the specific discharge capacity of the lignin carbon/nickel oxide nano composite material is 616mAh/g.

Fig. 1 is a constant current charge and discharge diagram of the lignin carbon/nickel oxide nanocomposite prepared in example 1 of the present invention, the first charge and discharge specific capacities of the lignin carbon/nickel oxide nanocomposite at a current density of 200mA/g are 912mAh/g and 1688mAh/g, the reversible specific capacity after 100 cycles is 1065mAh/g, and the capacity is basically kept stable in the subsequent cycle process, which is mainly benefited by the good dispersion of the nano nickel oxide, the good coating of the lignin carbon on the nano nickel oxide, and the synergistic effect of the nano nickel oxide and the nano lignin carbon on the electrochemical performance.

FIG. 2 is a rate performance diagram of the lignin carbon/nickel oxide nanocomposite prepared in example 1 of the present invention, and the specific discharge capacities of the lignin carbon/nickel oxide nanocomposite are 1066mAh/g, 930mAh/g, 720mAh/g, 585mAh/g, and 446mAh/g at current densities of 50mA/g, 100mA/g, 250mA/g, 500mA/g, and 1000mA/g, respectively. In addition, the current density can still be rapidly kept stable after being reduced from 1000mA/g to 50mA/g, and the specific discharge capacity is 1125mAh/g, which shows that the lignin carbon/nickel oxide nano composite material has excellent rate capability and reversibility and can be suitable for different working conditions.

FIG. 3 is an SEM image of a lignin carbon/nickel oxide nanocomposite prepared according to example 1 of the present invention. It can be seen from the figure that the particle size of the lignin carbon/nickel oxide nanocomposite is less than 10nm. The particle size distribution diagram can be obtained by carrying out statistical analysis on the particle sizes of the composite material particles in the figure, the average particle size of the composite material is 6.27nm, and the particle size of most particles is less than 7nm.

FIG. 4 is a TEM image of a lignin char/nickel oxide nanocomposite obtained in example 1 of the present invention. It can be observed from the figure that the nano nickel oxide particles are well dispersed and most of the nickel oxide particles have a particle size of less than 5nm.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A preparation method of a lignin carbon/nickel oxide nano composite material is characterized by comprising the following steps:

(1) Carrying out acid treatment on lignosulfonate by using a sulfuric acid solution with the mass concentration of 4-20%, collecting filtrate, adding an ethanol solution with the mass concentration of more than or equal to 50% to separate out precipitate, centrifuging and drying to obtain purified lignosulfonate with the sulfonation degree of more than 2.0 mmol/g;

(3) Carbonizing the lignin/nickel carbonate compound, then centrifugally washing and drying to obtain a lignin carbon/nickel oxide nano composite material;

in the step (2), the mass ratio of the purified lignosulfonate, carbonate, sulfanilate, nickel salt and aldehyde compound is 10g: 1-10 g: 0.5-10 g: 1-10 g:0.5 to 10g.

2. The method for preparing the lignin carbon/nickel oxide nanocomposite material according to claim 1, wherein the mass concentration of the solution obtained by dissolving the purified lignosulfonate in water in the step (2) is 10-40%; the mass concentration of the nickel salt solution is 5-20%; the mass concentration of the carbonate solution is 5-20%; the mass concentration of the sulfanilic acid salt solution is 10-40%; the mass concentration of the aldehyde compound solution is 20-50%.

3. The method for preparing the ligno-char/nickel oxide nanocomposite material according to claim 1, wherein the mass ratio of the purified lignosulfonate, carbonate, sulfanilate, nickel salt and aldehyde compound in the step (2) is 10g: 1-5 g: 0.5-2 g: 1-5 g: 0.5-2 g; the mass concentration of the sulfuric acid solution in the step (1) is 5-10%.

4. The preparation method of the lignin carbon/nickel oxide nanocomposite material according to claim 1, wherein the carbonization procedure in the step (3) is as follows: heating to 120-350 deg.c at 5 deg.c/min, maintaining for 20-60 min, heating to 500-700 deg.c at 5-10 deg.c/min, maintaining for 0.5-5 hr, and cooling to room temperature.

5. The method for preparing the lignin carbon/nickel oxide nanocomposite material according to claim 1, wherein the inorganic nickel salt in the step (2) is at least one of nickel chloride, nickel nitrate, nickel sulfate and nickel acetate; the carbonate is at least one of potassium carbonate, sodium carbonate, ammonium carbonate, potassium bicarbonate, sodium bicarbonate and ammonium bicarbonate; the aldehyde compound is at least one of formaldehyde, acetaldehyde and propionaldehyde.

6. The method for preparing the lignin carbon/nickel oxide nanocomposite as claimed in claim 1, wherein the addition rates of the carbonate solution, the sulfanilate solution, the nickel salt solution and the aldehyde compound solution in the step (2) are all 2-6 mL/min; the temperature of the hydrothermal treatment is 110-180 ℃, and the time is 1-4 h.

7. The method for preparing the lignin-carbon/nickel oxide nanocomposite according to claim 1, wherein the lignosulfonate in the step (1) is at least one of sodium lignosulfonate, calcium lignosulfonate and magnesium lignosulfonate extracted from red liquor of acid pulping and sulfonated alkali lignin and sulfomethylated alkali lignin obtained by sulfonating/sulfomethylating black liquor of alkaline pulping; the mass ratio of the lignosulfonate to the sulfuric acid solution to the ethanol solution is 1: 2.5-12.5: 2.5 to 5;

and (4) carbonizing in the step (3) under the atmosphere of nitrogen or inert gas.

8. The method for preparing the lignin carbon/nickel oxide nanocomposite material according to claim 2, wherein the mass concentration of the solution obtained by dissolving the purified lignosulfonate in water in the step (2) is 10-30%; the mass concentration of the nickel salt solution is 5-10%; the mass concentration of the carbonate solution is 5-10%; the mass concentration of the sulfanilic acid salt solution is 20-30%; the mass concentration of the aldehyde compound solution is 30-40%.

9. A lignin char/nickel oxide nanocomposite produced by the method of any one of claims 1 to 8.

10. The application of the lignin carbon/nickel oxide nanocomposite of claim 9 in the fields of lithium ion battery negative electrode materials, supercapacitors and photoelectrocatalysis.