Hard carbon negative electrode material, preparation method thereof, negative electrode and battery

Abstract

The application provides a hard carbon negative electrode material and a preparation method thereof, a negative electrode and a battery, and relates to the technical field of battery materials.The preparation method of the hard carbon negative electrode material comprises the following steps: providing an organic substance and a pore-forming oxidant; and mixing the pore-forming oxidant with the organic substance before carbonization of the organic substance, so that the pore-forming oxidant plays the roles of a pore-forming agent and an oxidant in the carbonization process of the organic substance; and the pore-forming oxidant is a strong-acid weak-base salt.The application also provides a hard carbon negative electrode material prepared based on the method, and a negative electrode and a battery based on the hard carbon negative electrode material.The technical scheme provided by the application improves the problem that the pore filling capacity and the embedding platform capacity of the hard carbon negative electrode material in the prior art are difficult to be simultaneously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a hard carbon negative electrode material, a preparation method thereof, a negative electrode and a battery. BACKGROUND

[0002] Due to the presence of Co, Fe, Ni, Mn and other key metal elements participating in the redox reaction in the positive electrode material, the price of the positive electrode material is long-term high, and the cost reduction space is limited, so seeking a lower-cost negative electrode material has become one of the main means to reduce the cost of the battery. The raw material source of the hard carbon negative electrode is wide, and the price is controllable. With the improvement of the reversible specific capacity and the initial efficiency of the hard carbon negative electrode material, the mass of the negative electrode material required by the battery with the same capacity is further reduced, so improving the reversible specific capacity of the hard carbon negative electrode is also one of the key means to reduce the cost of the secondary ion battery.

[0003] The storage mechanism of hard carbon for alkali metal ions can be divided into three categories: 1) adsorption capacity, 2) intercalation capacity, and 3) pore filling capacity. The adsorption capacity depends on the active functional groups on the surface of the material, and is positively correlated with the specific surface area and defect concentration of the material. However, too large specific surface area and too high defect concentration will significantly increase the irreversible capacity of the hard carbon negative electrode, resulting in low initial efficiency, which is not conducive to the improvement of the energy density of the full battery. Therefore, considering the comprehensive consideration of power density and initial efficiency, the size of the adsorption capacity needs to be reasonably controlled, and there are limitations for the improvement of the alkali metal ion storage of hard carbon. Therefore, the improvement of intercalation capacity and pore filling capacity has become one of the main means to improve the alkali metal ion storage of hard carbon. The intercalation capacity depends on the average interlayer spacing and the proportion of short-range ordered regions of the hard carbon material. For sodium ion batteries, in order to obtain a suitable sodium intercalation platform, the average interlayer spacing needs to be controlled between 0.37-0.42 nm; the pore filling capacity is the storage of sodium ions in the form of quasi-metal clusters in the microporous pores of the material, which puts high requirements on the pore volume and pore size distribution of the material.

[0004] Currently, in order to obtain a suitable embedded platform capacity, mainstream hard carbon raw materials such as biomass materials, resin materials, coal-based materials, etc. usually need to be oxidized. For example, patent CN118771355A crushes biomass materials, and then pre-oxidizes the materials in an air or oxygen atmosphere at a temperature of 240-280°C to improve the reversible sodium storage capacity of the biomass materials. Patent CN118458748A pre-treats starch and one or more of pitch, anthracite, resin and lignin in a gas containing oxygen. There are also patents that directly add strong oxidizing agents such as ammonium persulfate, potassium permanganate, concentrated sulfuric acid and hydrogen peroxide to the reaction system to oxidize the raw materials (CN117059759A). In order to obtain a suitable pore filling capacity, the material needs to be treated to form pores. For example, patent CN118619272A adds NaOH and KCl pore-forming agents to pitch-based raw materials to improve the sodium storage capacity of pitch-derived hard carbon negative electrodes. There are also patents that select boric acid, phosphoric acid and citric acid (CN118289757A, CN118458742A) as pore-forming agents. These strategies usually only focus on the regulation of pore filling capacity or embedded capacity, and it is difficult to simultaneously improve both forms of platform capacity, so the improvement of the total platform capacity is also limited. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of a hard carbon negative electrode material, which can simultaneously improve the pore filling capacity and the embedded capacity of the hard carbon negative electrode material.

[0006] Another purpose of the present application is to provide a hard carbon negative electrode material.

[0007] Still another purpose of the present application is to provide a negative electrode.

[0008] Still another purpose of the present application is to provide a battery.

[0009] In a first aspect, the present application provides a preparation method of a hard carbon negative electrode material, comprising the following steps:

[0010] providing an organic matter and a pore-forming oxidizing agent;

[0011] mixing the pore-forming oxidizing agent with the organic matter before carbonization of the organic matter, so that the pore-forming oxidizing agent plays the role of a pore-forming agent and an oxidizing agent during carbonization of the organic matter;

[0012] The pore-forming oxidizing agent is a strong acid-weak base salt.

[0013] Further, in some embodiments of the present application, the organic matter is mixed with the pore-forming oxidizing agent, and the pH value of the formed mixture is controlled to be not higher than 7.

[0014] Further, in some embodiments of the present application, the mass ratio of the organic matter to the pore-forming oxidant is (2-60):1.

[0015] Further, in some embodiments of the present application, the strong acid anion in the pore-forming oxidant is selected from one or more of sulfate or nitrate; and the weak base cation in the pore-forming oxidant is selected from metal cations of Group IIA-IVA and Group IB-VIIB.

[0016] Further, in some embodiments of the present application, the carbonization comprises a first carbonization process and a second carbonization process performed in sequence.

[0017] The carbonization temperature of the first carbonization process is lower than the carbonization temperature of the second carbonization process, and the temperature of the first carbonization process is not higher than 900°C.

[0018] Further, in some embodiments of the present application, the carbonization temperature of the first carbonization process is 500-900°C; and / or

[0019] The carbonization temperature of the second carbonization process is 1100-1700°C; and / or

[0020] The carbonization atmosphere of the first carbonization process is an inert gas environment; and / or

[0021] The carbonization atmosphere of the second carbonization process is an inert gas environment; and / or

[0022] The temperature rising rate in the first carbonization process is 1-10°C / min; and / or

[0023] The temperature rising rate in the second carbonization process is 3-20°C / min.

[0024] Further, in some embodiments of the present application, between the first carbonization process and the second carbonization process, a crushing process and an acid washing process are further included.

[0025] The first carbon material obtained from the first carbonization process is crushed and subjected to the acid washing process to obtain a second carbon material with a D50 of 1-20 μm and a pH value in the range of 5-8.

[0026] The second carbon material is dried and then subjected to the second carbonization process.

[0027] In a second aspect, the present application further provides a hard carbon negative electrode material, which is prepared by the preparation method of the hard carbon negative electrode material according to the first aspect.

[0028] In a third aspect, the application further provides a negative electrode comprising the hard carbon negative electrode material prepared by the preparation method of the hard carbon negative electrode material according to the first aspect or the hard carbon negative electrode material according to the second aspect.

[0029] In a fourth aspect, the application further provides a battery comprising the negative electrode according to the third aspect.

[0030] The hard carbon negative electrode material and the preparation method, the negative electrode and the battery provided by the embodiments of the application have the following advantages: the hard carbon negative electrode material is prepared by mixing a strong acid-weak base salt with an organic material as a raw material before carbonization in the preparation process, so that the strong acid-weak base salt gradually diffuses into the carbon material during the mixing or carbonization process (before the hard carbon material is completely formed) and continuously hydrolyzes and simultaneously undergoes a local oxidation-reduction reaction in the raw material or the carbon material during the carbonization process, so that the strong acid-weak base salt simultaneously plays the roles of a pore-forming agent and an oxidizing agent in the raw material or the carbon material, and the pore filling capacity and the intercalation capacity of the hard carbon negative electrode material are improved.

[0031] The hard carbon negative electrode material provided by the application has high pore filling capacity and intercalation capacity, and the intercalation capacity accounts for a high proportion in the storage of alkali metal ions in the hard carbon negative electrode material, which is beneficial to the improvement of the working voltage and the energy density of the ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 FIG. 1 is a SEM image of the hard carbon negative electrode material prepared by the embodiment 1 provided by the application;

[0033] Figure 2 FIG. 2 is a TEM image of the hard carbon negative electrode material prepared by the embodiment 1 provided by the application;

[0034] Figure 3 FIG. 3 is a first cycle charge-discharge curve of the hard carbon negative electrode material prepared by the embodiment 1, the comparative example 1 and the comparative example 2 provided by the application;

[0035] Figure 4 FIG. 4 is a comparison diagram of the platform capacity and the slope capacity of the hard carbon negative electrode material prepared by the embodiment 1, the comparative example 1 and the comparative example 2 provided by the application;

[0036] Figure 5 FIG. 5 is a SEM image of the hard carbon negative electrode material prepared by the comparative example 3 provided by the application. DETAILED DESCRIPTION

[0037] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the following will be combined with the accompanying drawings for clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0038] As used herein the terms "about" and "substantially" mean approximately or nearly, as in "about 90%," "substantially similar," or "substantially parallel."

[0039] "Made from" is synonymous with "comprising". The terms "comprise", "comprising", "include", "including", "have", "having", or any other variation thereof, used in this application and patents related hereto, cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0040] When mass fraction, concentration, or other value or parameter is expressed by a range, a preferred range, or a range of upper preferred values and lower preferred values, it is understood that all ranges formed by any pair of an upper limit or a preferred value and a lower limit or a preferred value, whether or not the range is separately disclosed, are specifically disclosed. For example, when a range "1-5" is disclosed, the described range should be interpreted to include small ranges or multiple small ranges formed by the end values being integers or fractions, such as "1-4", "1-3", "1-2", "1-2 and 4-5", "1-3 and 4-5", etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include all integers and fractions within the range.

[0041] In these embodiments, unless otherwise specified, the parts and percentages are by mass.

[0042] "Mass parts" refers to a basic unit of measurement representing the mass ratio relationship of multiple components, 1 part can represent any unit mass, such as 1 g, 2.689 g, etc. If we say that the mass parts of component A is a parts, and the mass parts of component B is b parts, it means that the mass ratio of component A to component B is a:b. Alternatively, it means that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number, indicating a multiple factor). It should not be misunderstood that unlike mass parts, the sum of the mass parts of all components is not limited to 100 parts.

[0043] "and / or" is used to indicate that one or both of the described situations can occur, for example, A and / or B includes (A and B) and (A or B).

[0044] The embodiments of the present application will be described in detail below with specific examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions are not specified in the examples, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be obtained by commercial purchase.

[0045] In the prior art, in order to improve the alkali metal ion storage capacity of the hard carbon negative electrode material, the hard carbon negative electrode material is usually selected to be pore-formed to improve the pore filling capacity, or the interlayer spacing is controlled to improve the intercalation platform capacity. However, the pore-forming strategy to improve the pore filling capacity and the oxidation strategy to improve the intercalation platform capacity in the prior art are often incompatible, resulting in that the pore filling capacity and the intercalation platform capacity of the hard carbon negative electrode material are difficult to be improved at the same time, and further resulting in that the overall capacity of the material is not obviously improved, and the proportion of the platform capacity is also difficult to be improved.

[0046] Based on the technical defects in the prior art, the present application provides a material preparation method for simultaneously improving the pore filling capacity and the intercalation platform capacity of the hard carbon negative electrode material. The weak base cations and the acid radical ions with strong oxidizing property, which are formed by hydrolysis of the strong acid weak base salt diffused into the raw material, locally undergo redox reaction in the raw material, realizing micro-zone pore formation and interlayer spacing control in the hard carbon negative electrode, and simultaneously improving the pore filling capacity and the intercalation platform capacity of the obtained hard carbon negative electrode material. The specific scheme is as follows:

[0047] An organic matter and a pore-forming oxidizing agent are provided.

[0048] Before the carbonization of the organic matter, the pore-forming oxidizing agent is mixed, so that the pore-forming oxidizing agent plays the roles of pore-forming agent and oxidizing agent in the carbonization process of the organic matter.

[0049] The pore-forming oxidizing agent is a strong acid weak base salt.

[0050] In the present application, the organic matter is a natural organic matter or an industrial organic matter or a biomass material used for carbonization to form a hard carbon material, such as one or more of starch, cellulose, lignin, resin, coal; a biomass material mainly composed of cellulose and lignin, such as one or more of walnut shell, bamboo powder, sugarcane residue, straw, etc.

[0051] The organic material should be clean powder or granular, non-powder or granular organic material can be cleaned, broken and mixed with pore-forming oxidant, so that the organic material is uniformly mixed with the pore-forming oxidant, which is beneficial to the diffusion of the pore-forming oxidant and the uniform entry of the organic material into the carbon material. For example, the organic material is broken into 30-500 mesh fine particles. Some organic materials in powder form do not need to be broken, such as purified corn starch, wheat starch, sweet potato starch and other starches, which usually have small particle size and can be used directly.

[0052] It should be further pointed out that the organic material provided in the present application can not need to be subjected to strict drying procedures, and a certain water content during mixing with the pore-forming oxidant is more beneficial to the pore formation and interlayer spacing control of the hard carbon material, especially for the organic material which is mixed by dry mixing. For example, the water content in the organic material provided in the present application can be not less than 1%, more preferably not less than 10%.

[0053] In the present application, the pore-forming oxidant used is a strong acid weak base salt, wherein the strong acid anion in the pore-forming oxidant is an oxidizing acid anion, such as one or more of sulfate or nitrate; the weak base cation in the pore-forming oxidant is selected from group IIA-IVA and group IB-VIIB metal cations, such as aluminum ion, iron ion, cobalt ion, manganese ion, copper ion, magnesium ion, bismuth ion, zinc ion, etc. For example, the pore-forming oxidant is selected from one or more of metal sulfate such as zinc sulfate, stannous sulfate, magnesium sulfate, ferrous sulfate, iron sulfate, aluminum sulfate, copper sulfate, cobalt sulfate, manganese sulfate, bismuth sulfate, and metal nitrate such as zinc nitrate, magnesium nitrate, iron nitrate, aluminum nitrate, copper nitrate, cobalt nitrate, manganese nitrate, bismuth nitrate.

[0054] In the present application, the mixing of the organic material and the pore-forming oxidant can be dry mixing or wet mixing. The dry mixing is that the organic material and the pore-forming oxidant are uniformly mixed by existing mixing equipment such as ball mill or planetary mixer, and the mixing time, stirring speed and mixing equipment are not limited, for example, the organic material and the pore-forming oxidant can be mixed at room temperature for 2-12 h by ball mill equipment. When the dry mixing process is used, the organic material and the pore-forming oxidant do not need to be strictly dried before mixing, so that a certain water content or crystal water is maintained in the organic material and the pore-forming oxidant, which is more beneficial to the hydrolysis of the pore-forming oxidant by free water and crystal water during the subsequent carbonization process, so as to express the characteristics of weak base and strong oxidizing acid. At this time, the water content in the organic material can be not less than 1%, more preferably not less than 10%; the water content or crystal water content in the pore-forming oxidant is also preferably not less than 10%.

[0055] When wet mixing is adopted, the organic material and the pore-forming oxidant are dispersed / dissolved in water respectively or simultaneously, and then the mixture is stirred uniformly and dried to obtain a mixed raw material. The drying method can be any existing drying method, such as evaporation drying, spray drying, belt drying, etc. Similarly, the water content or crystal water content in the mixed raw material after drying also does not need to be strictly controlled in an extremely low range, and a part of free water or crystal water can also be retained.

[0056] In the mixing process, the mass ratio of the organic material and the pore-forming oxidant in the suspension system formed by the organic material and the pore-forming oxidant is between 10% and 80%. The mass ratio can be adjusted according to the particle size, porosity, bulk density, and hydrophilicity of the organic material, so that the pore-forming oxidant is uniformly mixed with the organic material. In addition, in the wet mixing process, the pH value of the suspension system formed by the organic material and the pore-forming oxidant is controlled as much as possible in the range of <7, so as to avoid the precipitation of the pore-forming oxidant in the system, which is not conducive to the exertion of the strong oxidizing property of the pore-forming oxidant. In addition, the precipitation of a large amount of pore-forming oxidant can also cause agglomeration, so that the organic material and the pore-forming oxidant are not uniformly mixed, which is not conducive to the uniform distribution of the pore-forming oxidant in the mixed raw material formed by drying, and further affects the uniformity of the pores in the hard carbon material formed by carbonization, and affects the alkali metal ion storage capacity and other electrical properties of the hard carbon material. When zinc sulfate or zinc nitrate is used as the pore-forming oxidant, zinc ions are easy to precipitate in the form of Zn(OH)2 in a system with a high OH - ion concentration, which can cause the agglomeration of the precipitates, destroy the uniform mixing of the hard carbon precursor, and finally cause the uneven distribution of the pore-forming agent in the hard carbon after heat treatment.

[0057] When the organic material and the pore-forming oxidant are mixed, the mass ratio of the organic material to the pore-forming oxidant can be in the range of (2-60):1, preferably (2-40):1, and more preferably (3-30):1. The amount of the pore-forming oxidant should not be too low or too high. If the amount of the pore-forming oxidant is too low, the treatment effect cannot be guaranteed. If the amount of the pore-forming oxidant is too high, the cost will be significantly increased, and the agglomeration of the pore-forming particles will be caused, the pore size of the material will be increased, the capacity of the high-pressure area will be significantly increased, and the initial efficiency may also be decreased.

[0058] After the organic material and the pore-forming oxidant are uniformly mixed to form a mixed raw material, the carbonization process can be carried out.

[0059] In the present application, the hard carbon material is obtained after the mixed raw material is carbonized twice by the first carbonization process and the second carbonization process. In the first carbonization process, the carbonization temperature is low, so that the organic material is not completely carbonized, and the first carbon material formed has a low density. In the second carbonization process, the carbonization temperature is high, so that the hard carbon negative electrode material with a high density is formed.

[0060] In the first carbonization process, the carbonization temperature is not higher than 900°C; while in the second carbonization process, the carbonization temperature is not lower than 1100°C. In the first carbonization process, the heating rate is controlled in a slower range, such as 1-10°C / min, while in the second carbonization process, the heating rate can be appropriately increased, such as 3-20°C / min. Preferably, the heating rate in the first carbonization process is lower than that in the second carbonization process. More preferably, the heating rate in the first carbonization process is 1-5°C / min, and the heating rate in the second carbonization process is 5-15°C / min. The carbonization atmosphere in the first carbonization process and the second carbonization process can be a protective gas atmosphere or an inert gas atmosphere, such as nitrogen, helium, neon, argon, krypton, etc. The carbonization time can be adjusted according to the material. For example, the carbonization time of the first carbonization process is 1-8h, preferably 2-5h; and the carbonization time of the second carbonization process is 1-5h, preferably 2-4h.

[0061] In the carbonization process, controlling the heating rate and carbonization temperature of the first carbonization process to be lower can make the pore filling capacity and the embedding platform capacity of the obtained hard carbon negative electrode material both have more excellent improvement. The reason can be that: in the mixing process of the organic matter and the pore-forming oxidant, the pore-forming oxidant is mixed with the organic matter, and in the mixing process and / or the heating process of the first carbonization process, the pore-forming oxidant diffuses or penetrates into the interior of the organic matter, such as the layered structure of starch crystal / amorphous region, the chain structure of cellulose and lignin, the pores of resin and coal-based materials, and under the action of crystal water or free water or water molecules generated by the decomposition of the organic matter in the carbonization process, hydrolysis occurs, and then a local strong acid region is formed in the interior of the organic matter, which oxidizes the material; and the weak base generated by it further decomposes at a higher temperature to form a metal oxide, which acts as a pore-forming template in the interior of the material and reacts with the carbon material formed by carbonization to form pores, so that the pore-forming oxidant can act as an oxidant and a pore-forming agent.

[0062] Taking zinc sulfate as an example of the pore-forming oxidant, in the first carbonization process, zinc sulfate enters the interior of the organic matter, and continuously reacts under the action of crystal water / free water or water molecules generated by decomposition as follows:

[0063]

[0064] A number of strong oxidizing sulfuric acid and precipitated zinc hydroxide microzones are formed in the interior of the organic matter, in which the strong acid oxidizes the material; and as the temperature rises, the precipitated zinc hydroxide gradually decomposes to form zinc oxide, and reacts with the carbon formed by carbonization of the organic matter to form a porous hard carbon negative electrode. The specific reaction process is as follows:

[0065] Zn(OH)2→ ZnO + H2O↑

[0066] ZnO + C → Zn + CO↑.

[0067] It should be noted that the pore-forming oxidant in the present application adopts a strong acid-weak base salt, wherein the acid radical should be a strong acid radical with oxidizing property, and the metal cation should be a non-strong alkaline metal cation which can form a precipitate in an alkaline aqueous solution.

[0068] The first carbonization process and the second carbonization process further comprise a crushing process, in which the first carbon material generated in the first carbonization process is crushed to have a particle size D50 of 1 μm to 20 μm, and then the second carbonization process is performed.

[0069] In some other embodiments, the crushing process is followed by an acid pickling process to remove the metal generated by the pore-forming oxidant in the first carbon material, and then drying, and then entering the second carbonization process. The acid pickling process is not essential to the present application, and can be selected according to the vaporization temperature of the metal formed by the metal cation in the pore-forming oxidant. When the vaporization temperature of the metal formed by the selected metal cation is lower than the carbonization temperature of the second carbonization process, the acid pickling process is not needed. When the vaporization temperature of the metal formed by the selected metal cation is equal to or higher than the carbonization temperature of the second carbonization process, the acid pickling process is provided. For example, ZnO can be reduced to elemental zinc at about 800°C, and the boiling point of elemental zinc is about 900°C, so that elemental zinc can slowly vaporize when carbonization is performed at a temperature higher than 1000°C. Therefore, when zinc nitrate or zinc sulfate is used as the pore-forming oxidant, the steps of acid pickling and drying are not needed.

[0070] The acid pickling process can use an acid which can dissolve the corresponding metal, such as one or more of hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid. The acid pickling temperature can be room temperature, or the acid pickling can be performed with appropriate heating, and is preferably 40-80°C. After acid pickling, the carbon material obtained is dried and then subjected to the second carbonization process. The drying process can be any drying process in the prior art, such as flash drying, belt drying, drum drying, etc., and is preferably flash drying.

[0071] In a second aspect, the present application further provides a hard carbon negative electrode material, which is prepared by the preparation method of the hard carbon negative electrode material according to the first aspect.

[0072] In a third aspect, the present application further provides a negative electrode, which comprises the hard carbon negative electrode material prepared by the preparation method of the hard carbon negative electrode material according to the first aspect, or the hard carbon negative electrode material according to the second aspect.

[0073] In a fourth aspect, the application also provides a battery comprising the negative electrode of the third aspect, which can be a sodium-ion battery or a lithium-ion battery.

[0074] In order to facilitate the understanding of the innovative points of the hard carbon negative electrode material, the preparation method thereof, the battery and the electrical equipment provided by the present application by those skilled in the art, some preferred embodiments are provided below in conjunction with the drawings to illustrate the above technical solutions.

[0075] Embodiment 1

[0076] The embodiment provides a preparation method of a hard carbon negative electrode material, comprising the following steps:

[0077] (1) 100 g of corn starch is dispersed in 150 mL of deionized water, and then 15 g of zinc sulfate is added and stirred to dissolve uniformly; after stirring for 1 h, the suspension is placed in an 80℃ oil bath, and stirring evaporation drying is performed, and after grinding, a uniformly mixed precursor powder is obtained;

[0078] (2) The precursor powder is heated to 700℃ at a heating rate of 2℃ / min under a nitrogen atmosphere, and is kept for 2 h for pre-carbonization;

[0079] (3) The pre-carbonized material is ground in an air flow pulverizer, and the D50 of the discharged sample is controlled to be 6 μm;

[0080] (4) The ground sample is heated to 1300℃ at a heating rate of 5℃ / min under a nitrogen atmosphere, and is kept for 3 h for final carbonization, and the hard carbon negative electrode material is obtained.

[0081] Embodiment 2

[0082] The embodiment provides a preparation method of a hard carbon negative electrode material, comprising the following steps:

[0083] (1) 100 g of corn starch is dispersed in 150 mL of deionized water, and then 15 g of zinc nitrate is added and stirred to dissolve uniformly; after stirring for 1 h, the suspension is placed in an 80℃ oil bath, and stirring evaporation drying is performed, and after grinding, a uniformly mixed precursor powder is obtained;

[0084] (2) The precursor powder is heated to 700℃ at a heating rate of 2℃ / min under a nitrogen atmosphere, and is kept for 2 h for pre-carbonization;

[0085] (3) The pre-carbonized material is ground in an air flow pulverizer, and the D50 of the discharged sample is controlled to be 6 μm;

[0086] (4) The sample after the grinding treatment is heated to 1300°C at a heating rate of 5°C / min under a nitrogen atmosphere, and heat preservation is performed for 3h to perform final carbonization, and the hard carbon negative electrode material is obtained.

[0087] Example 3:

[0088] The embodiment provides a preparation method of a hard carbon negative electrode material, and comprises the following steps:

[0089] (1) 100g of corn starch is dispersed in 150mL of deionized water, and then 15g of stannous sulfate is added and uniformly dissolved by stirring; after stirring for 1h, the suspension is placed in an 80°C oil bath, and the suspension is evaporated and dried by stirring, and then ground to obtain a uniformly mixed precursor powder;

[0090] (2) The precursor powder is heated to 700°C at a heating rate of 2°C / min under a nitrogen atmosphere, and heat preservation is performed for 2h to perform pre-carbonization;

[0091] (3) The pre-carbonized material is ground in an air flow crusher, and the D50 of the discharged sample is controlled to be 6μm;

[0092] (4) The sample after the grinding treatment in step 3 is subjected to acid washing and purification, the volume ratio of the components in the mixed acid used is hydrochloric acid:sulfuric acid = 7:3, the solid content in the acid washing solution is 35%, and the acid washing temperature is 65°C. After the acid washing is completed, deionized water is repeatedly washed until the pH reaches 5-8, and then the filter cake is obtained by pressure filtration, and the dried powder is obtained by using a flash drying machine;

[0093] (5) The sample after the grinding treatment is heated to 1300°C at a heating rate of 5°C / min under a nitrogen atmosphere, and heat preservation is performed for 3h to perform final carbonization, and the hard carbon negative electrode material is obtained.

[0094] Example 4:

[0095] The embodiment provides a preparation method of a hard carbon negative electrode material, and comprises the following steps:

[0096] (1) 100g of cellulose is dispersed in 200mL of deionized water, and then 20g of ferric nitrate is added and uniformly dissolved by stirring; after stirring for 1h, spray drying is performed to obtain a uniformly mixed precursor powder;

[0097] (2) The precursor powder is heated to 600°C at a heating rate of 3°C / min under a nitrogen atmosphere, and heat preservation is performed for 3h to perform pre-carbonization;

[0098] (3) The pre-carbonized material is ground in an air flow crusher, and the D50 of the discharged sample is controlled to be 5.5μm;

[0099] (4) The sample after the grinding treatment in step 3 is subjected to acid washing and purification, the volume ratio of components in the mixed acid used is hydrochloric acid:sulfuric acid = 7:3, the solid content in the acid washing solution is 35%, and the acid washing temperature is 65°C. After the acid washing is completed, the sample is repeatedly washed with deionized water until the pH reaches 5-8, then pressure filtration is performed to obtain a filter cake, and a flash drying machine is used to obtain a dried powder;

[0100] (5) The sample after the grinding treatment is heated to 1400°C at a heating rate of 10°C / min under a nitrogen atmosphere, and heat preservation is performed for 2h to perform final carbonization, thereby obtaining the hard carbon negative electrode material.

[0101] Example 5:

[0102] The embodiment provides a preparation method of a hard carbon negative electrode material, comprising the following steps:

[0103] (1) The waste bagasse is washed 2-3 times with deionized water to remove impurities such as sludge on the surface, and then dried; then the dried bagasse is crushed, and the particle size interval of the sample is controlled to be about 100 mesh;

[0104] (2) 100g of the crushed bagasse is dispersed in 300mL of deionized water, and then 30g of nickel sulfate is added and stirred to dissolve uniformly; after stirring for 1h, spray drying is performed to obtain a uniformly mixed precursor powder;

[0105] (3) The precursor powder is heated to 700°C at a heating rate of 3°C / min under a nitrogen atmosphere, and heat preservation is performed for 2h to perform pre-carbonization;

[0106] (4) The material after pre-carbonization is ground in an airflow pulverizer, and the D50 of the discharged sample is controlled to be 5μm;

[0107] (5) The sample after the grinding treatment in step 4 is subjected to acid washing and purification, the volume ratio of components in the mixed acid used is hydrochloric acid:hydrofluoric acid:sulfuric acid = 7:2:1, the solid content in the acid washing solution is 20%, and the acid washing temperature is 75°C. After the acid washing is completed, the sample is repeatedly washed with deionized water until the pH reaches 5-8, then pressure filtration is performed to obtain a filter cake, and a flash drying machine is used to obtain a dried powder;

[0108] (6) The sample after the grinding treatment is heated to 1250°C at a heating rate of 15°C / min under a nitrogen atmosphere, and heat preservation is performed for 3h to perform final carbonization, thereby obtaining the hard carbon negative electrode material.

[0109] Example 6:

[0110] The embodiment provides a preparation method of a hard carbon negative electrode material, comprising the following steps:

[0111] (1) Take anthracite block to crush, the particle size interval of sample is controlled at about 300 mesh;

[0112] (2) Take 100g of the pulverized anthracite, disperse in 80mL deionized water, then add 8g of copper nitrate, stir to dissolve uniformly; after stirring for 1h, spray drying is carried out to obtain a uniformly mixed precursor powder;

[0113] (3) The precursor powder is heated to 800℃ at a heating rate of 5℃ / min under a nitrogen atmosphere, and kept for 1h to perform pre-carbonization;

[0114] (4) The pre-carbonized material is ground in an air jet mill, and the D50 of the discharged sample is controlled to be about 7μm;

[0115] (5) The sample after the grinding treatment in step 4 is subjected to acid pickling purification, and the volume ratio of each component in the mixed acid used is hydrochloric acid:hydrofluoric acid:sulfuric acid = 6:3:1, the solid content in the acid pickling solution is 40%, and the acid pickling temperature is 55℃. After acid pickling, deionized water is repeatedly washed until the pH reaches 5-8, then pressure filtration is performed to obtain a filter cake, and a flash drying machine is used to obtain a dried powder;

[0116] (6) The ground sample is heated to 1150℃ at a heating rate of 8℃ / min under a nitrogen atmosphere, and kept for 2h to perform final carbonization, thereby obtaining the hard carbon negative electrode material.

[0117] Example 7:

[0118] The embodiment provides a preparation method of a hard carbon negative electrode material, comprising the following steps:

[0119] (1) Take resin block to crush, the particle size interval of sample is controlled at about 300 mesh;

[0120] (2) Take 100g of the pulverized resin, disperse in 80mL deionized water, then add 15g of cobalt sulfate, stir to dissolve uniformly; after stirring for 1h, spray drying is carried out to obtain a uniformly mixed precursor powder;

[0121] (3) The precursor powder is heated to 700℃ at a heating rate of 3℃ / min under a nitrogen atmosphere, and kept for 2h to perform pre-carbonization;

[0122] (4) The pre-carbonized material is ground in an air jet mill, and the D50 of the discharged sample is controlled to be about 5.8μm;

[0123] (5) The sample after the grinding treatment in step 4 is subjected to acid pickling purification, and the volume ratio of components in the mixed acid used is hydrochloric acid:hydrofluoric acid:sulfuric acid = 8:1:1, the solid content in the acid pickling solution is 40%, and the acid pickling temperature is 65°C. After the acid pickling is completed, the sample is repeatedly washed with deionized water until the pH reaches 5-8, and then pressure filtration is performed to obtain a filter cake, and a flash drying machine is used to obtain a dried powder;

[0124] (6) The sample after the grinding treatment is heated to 1300°C at a heating rate of 10°C / min under a nitrogen atmosphere, and held for 2h to perform final carbonization, thereby obtaining the hard carbon negative electrode material.

[0125] Example 8

[0126] The present example provides a preparation method of a hard carbon negative electrode material. Compared with Example 1, the preparation method uses corn starch and zinc sulfate to mix in a dry mixing manner. The specific mixing steps are as follows:

[0127] 100g of commercially available corn starch with a water content of about 10% is added to a ball mill tank, and then 15g of zinc sulfate is added. The ball milling medium is zirconia grinding ball, the rotation speed is 220rmp / min, and the mixing time is 2h to obtain a uniformly mixed precursor powder. The remaining preparation steps are the same as those in Example 1 to obtain the hard carbon negative electrode material.

[0128] Comparative Example 1

[0129] Compared with Example 1, the present comparative example uses zinc chloride as a pore-forming oxidant, and the remaining steps are the same as those in Example 1 to obtain a hard carbon negative electrode material for comparison.

[0130] Comparative Example 2

[0131] Compared with Example 1, the present comparative example uses sodium sulfate as a pore-forming oxidant, and the remaining steps are the same as those in Example 1 to obtain a hard carbon negative electrode material for comparison.

[0132] Comparative Example 3

[0133] Compared with Example 1, the present comparative example adds 1mol / L NaOH solution dropwise to the mixed solution system after mixing corn starch and zinc sulfate in step (1), and adjusts the pH of the mixed solution to 10. After stirring for 1h, the suspension is placed in an 80°C oil bath, and stirring evaporation drying is performed. After grinding, a uniformly mixed precursor powder is obtained. The remaining steps are the same as those in Example 1 to obtain a hard carbon negative electrode material for comparison.

[0134] Comparative Example 4

[0135] Compared with Example 1, the present comparative example mixes the pore-forming oxidant after the first carbonization process with the carbon material. The specific steps are as follows:

[0136] (1) Take 100 g of corn starch, heat to 700℃ at a heating rate of 2℃ / min under a nitrogen atmosphere, and pre-carbonize for 2 h;

[0137] (2) The pre-carbonized material is ground in an air flow grinder, and the D50 of the discharged sample is controlled to be about 6 μm;

[0138] (3) The ground sample is dispersed in 150 mL of deionized water, and 15 g of zinc sulfate is added and stirred to dissolve uniformly. After stirring for 1 h, the suspension is placed in an 80℃ oil bath, and stirred to evaporate and dry. After grinding, a uniformly mixed powder is obtained;

[0139] (4) Heat to 1300℃ at a heating rate of 5℃ / min under a nitrogen atmosphere, and final-carbonize for 3 h to obtain the hard carbon negative electrode material for comparison.

[0140] Comparative Example 5

[0141] The pore-forming oxidant used in this comparative example is zinc acetate, and the other steps are the same as in Example 1 to obtain the hard carbon negative electrode material for comparison.

[0142] Comparative Example 6

[0143] The amount of starch used in this comparative example is the same as in Example 1, and the amount of zinc sulfate added is 100 g (organic matter:pore-forming oxidant = 1:1), and the other steps are the same as in Example 1 to obtain the hard carbon negative electrode material for comparison.

[0144] Comparative Example 7

[0145] The amount of starch used in this comparative example is the same as in Example 1, and the amount of zinc sulfate added is 1 g (organic matter:pore-forming oxidant = 100:1), and the other steps are the same as in Example 1 to obtain the hard carbon negative electrode material for comparison.

[0146] Comparative Example 8

[0147] The heating rate of the first carbonization step in this comparative example is 15℃ / min, and the other steps are the same as in Example 1 to obtain the hard carbon negative electrode material for comparison.

[0148] Test Methods:

[0149] (1) Electrochemical sodium storage performance test

[0150] The hard carbon material prepared in the above examples and comparative examples was mixed with sodium alginate (SA) in a mass ratio of 95:5 as an active material, and then a proper amount of deionized water was added dropwise to prepare a slurry with a suitable viscosity, which was coated on a copper foil. After drying in a vacuum oven at 100°C for 12 hours, the copper foil was taken out and cut into a circular piece with a diameter of 12 mm, and then assembled into an alkali metal ion battery. The electrolyte was 1M NaPF6 / (EC / DEC, volume ratio 1:1), and Whatman glass fiber was used as a separator. The battery was assembled in a glove box filled with high-purity argon. The electrochemical sodium storage performance was tested on a Wuhan Lanbote CT2001A battery tester, and the charge-discharge voltage was 0-3.0V. The charge-discharge rate was 0.1C (1C=300mA / g). The first cycle discharge specific capacity and charge specific capacity were recorded, and the first cycle coulombic efficiency was calculated. (First cycle coulombic efficiency=first cycle charge specific capacity / first cycle discharge specific capacity)

[0151] (2) SEM scanning electron microscope test

[0152] The conductive glue was pasted on the sample stage, and then a small amount of powder was clamped with tweezers and adhered to the conductive glue. The excess powder was blown off with an ear bulb, and then the test was performed. The instrument used was Hitachi S4800.

[0153] (3) TEM transmission electron microscope test

[0154] A small amount of sample was ultrasonically dispersed in anhydrous ethanol, and then a small amount of solution was sucked with a pipette gun and dropped 1-2 drops from the vertical top of the microgrid, and then dried under a baking lamp for 10 min, and then the test was performed. The instrument used was Tecnai F20 (TF20).

[0155] The hard carbon negative electrode materials obtained in the above examples and comparative examples and the hard carbon negative electrode materials used for comparison were subjected to the above electrochemical test, and the test results are shown in Table 1 and Figures 1-5 .

[0156] Table 1

[0157]

[0158]

[0159] Result analysis:

[0160] As can be seen from Figure 1 , after the corn starch is uniformly mixed with a certain amount of zinc sulfate, even after heat treatment, the spherical morphology of the starch particles is maintained, which is significantly different from the flaky structure obtained by directly heat-treating the corn starch. As can be seen from the TEM image of Figure 2 , after adding zinc sulfate, a large number of mesoporous structures appear in the prepared material.

[0161] It can be found by comparing Examples 1-3 that the hard carbon material obtained by heat treatment after mixing corn starch with zinc sulfate or zinc nitrate or stannous sulfate uniformly exhibits a high reversible sodium storage capacity and a first-week coulombic efficiency. Further comparison of Example 1 with Comparative Examples 1-2 shows that the reversible capacity of Example 1 is increased by 55.8 and 41.6 mAh / g, respectively, relative to Comparative Examples 1 and 2, and the platform capacity (capacity below 0.1 V) is significantly improved. Figure 3 Figure 4 It can be found from the comparative bar chart that the platform capacity of Example 1 is as high as 273 mAh / g, while the platform capacities of Comparative Examples 1 and 2 are 210.2 and 190.2 mAh / g, respectively. Further mathematical conversion shows that the platform capacity of Example 1 accounts for 74.1%, while the values of Comparative Examples 1 and 2 are 67.3% and 56.9%, respectively. In addition, the first-week reversible capacity of the hard carbon negative electrode material obtained by using a weak acid-weak base salt in Comparative Example 5 is only 276.7 mAh / g, which is much lower than the reversible capacity of Example 1 under the same processing conditions. It can be known from the comparison that the addition of a reagent that can act as a pore-forming agent and an oxidizing agent in the reaction system can significantly improve the reversible sodium storage capacity and the platform capacity ratio of the prepared hard carbon material.

[0162] Examples 4-7 show that the strategy proposed in the present application is also applicable to cellulose, coal-based, resin-based, and sugarcane residue, etc. biomass materials, and has certain universality, and can be used to prepare hard carbon negative electrode materials with high sodium storage performance in different raw material systems.

[0163] ​The pH > 7 in the wet mixing process of Comparative Example 3 can cause the roughness of the surface of the hard carbon material to increase significantly, the particles to increase, and the distribution to be extremely uneven, which are caused by the rapid precipitation of metal cations, and the added reagent cannot play a good pore-forming and oxidizing effect in the alkaline environment system; the electrochemical performance of Comparative Example 3 and Comparative Example 4 shows that the inhibition of the pore-forming oxidant effect can significantly affect the sodium storage performance of the final hard carbon material. In addition, the pore-forming agent effect and the oxidant effect of the pore-forming oxidant are not obvious in Comparative Example 4, and the reason may be that the diffusion process and the hydrolysis process between the hard carbon precursor organizations in the wet mixing process, and the interaction between the adsorbed water or the crystallization water released by the raw materials or the water released by polymerization at the initial stage of heating, play an important role in the performance of the selected reagent. If the pore-forming oxidant is not added in the first carbonization process at 500-900℃, but is added in the second carbonization process at 1100-1700℃, the precursor has formed a relatively dense structure after pre-carbonization, and the added pore-forming oxidant cannot diffuse in the bulk phase of the material, but can only coat the surface of the material; moreover, the polymerization and dehydration stage of the material mainly occurs below 900℃, and the decomposition temperature of nitrate and sulfate is basically below 900℃, so the added pore-forming oxidant cannot play a role due to the inability to hydrolyze and the high-temperature decomposition. Therefore, in Comparative Example 4, the addition of the pore-forming oxidant in the second carbonization process cannot effectively improve the sodium storage performance of the material.

[0164] In addition, the applicant also discusses the optimization effect of the amount of the added pore-forming oxidant on the platform capacity of the obtained hard carbon negative electrode material, and it can be seen from Comparative Example 6 and Comparative Example 7 that too much pore-forming oxidant can also improve the charge and discharge capacity of the hard carbon negative electrode material, but the coulombic efficiency decreases significantly; and too little pore-forming oxidant cannot achieve obvious technical effects. In addition, it can be seen from Comparative Example 8 that the heating rate of the first carbonization process should not be too fast, and too fast heating rate is not conducive to the optimization effect of the pore-forming oxidant on the platform capacity of the negative electrode material.

[0165] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any changes or replacements that can be easily thought of by those skilled in the art within the technical range disclosed by the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing a hard carbon negative electrode material, comprising the following steps: providing an organic material and a pore-forming oxidant; mixing the pore-forming oxidant with the organic material before carbonization of the organic material, so that the pore-forming oxidant functions as a pore-forming agent and an oxidant during carbonization of the organic material; the pore-forming oxidant is a strong acid-weak base salt; the strong acid anion in the pore-forming oxidant is selected from one or more of sulfate or nitrate; the weak base cation in the pore-forming oxidant is selected from metal cations of Group IIA to Group IVA and Group IB to Group VIIB. 2.The method for preparing a hard carbon negative electrode material according to claim 1, wherein the organic material is mixed with the pore-forming oxidant wet, and the pH value of the mixture is controlled to be not higher than 7. 3.The method for preparing a hard carbon negative electrode material according to claim 1 or 2, wherein the mass ratio of the organic material to the pore-forming oxidant is (2-60) :

1. 4.The method for preparing a hard carbon negative electrode material according to claim 1, wherein the carbonization comprises sequentially performing a first carbonization process and a second carbonization process; the carbonization temperature of the first carbonization process is lower than the carbonization temperature of the second carbonization process, and the temperature of the first carbonization process is not higher than 900 ℃. 5.The method for preparing a hard carbon negative electrode material according to claim 4, wherein the carbonization temperature of the first carbonization process is 500-900 ℃; and / or the carbonization temperature of the second carbonization process is 1100-1700 ℃; and / or the carbonization atmosphere of the first carbonization process is an inert gas environment; and / or the carbonization atmosphere of the second carbonization process is an inert gas environment; and / or the temperature rising rate in the first carbonization process is 1-10 ℃ / min; and / or the temperature rising rate in the second carbonization process is 3-20 ℃ / min. The organic matter and the pore-forming oxidant are mixed by dry mixing or wet mixing. 12h; the water content in the organic matter is not less than 10%, and the water content / crystallization water content in the pore-forming oxidant is not less than 10%; when the organic matter and the pore-forming oxidant are wet mixed, the mass ratio of the organic matter and the pore-forming oxidant in the suspension system formed in the mixing process is between 10% and 80%. 6.The method for preparing a hard carbon negative electrode material according to claim 4, wherein between the first carbonization process and the second carbonization process, a crushing process and an acid pickling process are further included; the first carbon material obtained by the first carbonization process is crushed and acid-pickled to obtain a second carbon material with a D50 of 1-20 μm and a pH value in the range of 5-8; and the second carbon material is dried before the second carbonization process. 7.A hard carbon negative electrode material, prepared by the method for preparing a hard carbon negative electrode material according to any one of claims 1-6. 8.A negative electrode, comprising the hard carbon negative electrode material prepared by the method for preparing a hard carbon negative electrode material according to any one of claims 1-6 or the hard carbon negative electrode material according to claim 7. A negative electrode according to claim 8. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 9. A battery, characterized by ​

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